Main idea / best title

Pick the choice that covers the whole passage, not one detail

Scan back to the exact sentence that states it

The meaning of a word

Use the surrounding sentence (context) to define it

An inference / conclusion

Choose what the text supports — never outside knowledge

The purpose of a step

Find why the passage says the step is done

Driven teeth ÷ driver teeth; more teeth = slower, more torque

Force = pressure × area; same pressure throughout the fluid

Bearings/lubrication cut friction, wear, and heat

Stores rotational energy; smooths out power delivery

Over-speeding a belt causes slippage; tension transmits power

What sections are on the POSS exam?

Four tests: Reading Comprehension (36 questions, 30 minutes), Mathematical Usage (either 18 questions in 7 minutes or 46 questions in 17 minutes, depending on the battery), Mechanical Concepts (44 questions, 20 minutes), and Figural Reasoning (20 questions, 10 minutes). The whole battery takes about two hours to administer, including instructions and examples.

How is the POSS scored?

Each test is scored on the number of questions answered correctly, with no penalty for guessing — so you should answer every item. The four scores combine into a single EEI Aptitude Index from 0 to 15 that predicts plant-operations effectiveness. There is no universal pass mark; each hiring utility sets its own cutoff and ranks candidates by their index.

Can you use a calculator on the POSS?

No. The Mathematical Usage test is solved by hand, so practice mental math, unit conversions, and fraction-to-percent conversions until they're quick. The math itself is straightforward — the challenge is doing it accurately and fast within the time limit.

What is the difference between the POSS and the CAST?

Both are EEI selection tests, but the POSS is for power-plant operator jobs and the CAST is for construction and skilled-trade jobs. They share Reading Comprehension, Mathematical Usage, and Mechanical Concepts, but the POSS adds Figural Reasoning while the CAST instead has Graphic Arithmetic. (Assembling Objects is an ASVAB subtest and is not on either EEI test.)

What is on the Mechanical Concepts test?

Pictorial questions about mechanical principles — simple machines like pulleys, levers, and gears; hydraulics, pressure, and fluids; force, work, friction, and balance; and common plant equipment such as pumps, valves, motors, and bearings. Each item shows a mechanical situation and asks you to choose answer A, B, or C.

How many questions are on the POSS?

It depends on the battery. With the longer Mathematical Usage version the four tests total about 146 questions (36 + 44 + 46 + 20); with the shorter math version the total is about 118. EEI does not publish a single fixed total, so treat 146 as the long-form count for the most common battery.

How should I use this POSS study guide?

Work through the four test modules — Reading, Mathematical Usage, Mechanical Concepts, and Figural Reasoning — take each checkpoint to find your gaps, then drill your weakest area with our free practice questions and flashcards. Because each test is separately timed, rehearse your pacing on full, timed practice runs too.

Is this POSS study guide free?

Yes — the full guide, the checkpoints, the glossary, the practice questions, and the flashcards are 100% free, with no account required.

How do you find the main idea of a technical reading passage?

Read for what every sentence has in common, then state it in one sentence of your own. The main idea is the single point the whole passage supports; supporting details (numbers, steps, examples) back it up. Answer only from what the text says — not from outside plant knowledge you happen to have. POSS reading passages are the kind of material found in plant-operator training and safety manuals, so the answer is always in the passage. Beware choices that are true in real life but not stated in the text — only what the passage supports is correct.

What is the difference between a main idea and a supporting detail?

The main idea is the overall point of a passage; supporting details are the facts, examples, numbers, and steps that prove or explain it. A detail answers 'how do we know?' while the main idea answers 'what is this about?' Detail questions point to one line; main-idea questions cover the whole passage. For a detail question, scan back to the exact sentence that contains the fact rather than relying on memory. For a main-idea question, pick the choice that covers the whole passage, not just one paragraph.

How does a pulley system give you a mechanical advantage?

Count the rope segments that actually support the load — that number is the mechanical advantage. A fixed pulley (1 segment) only changes direction; a movable pulley (2 segments) halves the effort; a block-and-tackle with 4 segments cuts the effort to one-quarter. Effort = load divided by supporting segments. A machine never gives free work: what you save in force you pay back in the distance you must pull the rope. To lift a 300-pound load with a 4-segment block and tackle, you pull only about 75 pounds — but four times as much rope.

What are the three classes of lever?

Identify a lever by what sits in the middle. Class 1 has the fulcrum in the middle (a seesaw or crowbar). Class 2 has the load in the middle (a wheelbarrow) and always multiplies force. Class 3 has the effort in the middle (tweezers or your forearm) and trades force for speed and range. The law of the lever: effort times effort-arm equals load times load-arm, so a longer effort arm multiplies your force. Class 2 levers always give a mechanical advantage greater than 1; class 3 levers give an advantage less than 1.

How do meshed gears change speed and torque?

Two externally meshed gears turn in opposite directions. The gear with more teeth turns slower but with more torque; the smaller gear turns faster with less torque. The gear ratio is driven teeth divided by driver teeth — a 30-tooth gear driven by a 10-tooth gear turns one-third as fast with three times the torque. A gear reducer uses this trade to turn a fast, low-torque motor into slow, high-torque output for heavy machinery. An idler gear placed between two gears reverses the output direction but does not change the gear ratio.

How does a hydraulic system multiply force?

By Pascal's principle, pressure in a confined fluid is the same everywhere, so a small piston and a large piston share one pressure. Because force equals pressure times area, the larger piston's bigger area produces a much larger force. A 10-times-bigger output area gives 10 times the output force. Pressure equals force divided by area; a 50-pound push on a 2-square-inch piston makes 25 psi throughout the fluid. That same 25 psi acting on a 20-square-inch output piston produces 500 pounds of force — how jacks, presses, and plant actuators work.

What is the relationship between pressure, force, and area?

Pressure equals force divided by area (P = F / A). Rearranged, force equals pressure times area, and area equals force divided by pressure. The same force spread over a larger area makes less pressure; concentrated on a small area it makes more — which is why a sharp tip pierces and a flat foot does not. In a confined fluid, the pressure is the same at every point, so this relationship governs every hydraulic and pneumatic question. Keep your units consistent — pounds with square inches give pounds per square inch (psi).

How do you calculate a percentage increase?

Subtract to find the change, then divide the change by the original amount and multiply by 100. If a turbine's output rises from 150 MW to 180 MW, the change is 30 MW; 30 divided by 150 is 0.20, so it's a 20% increase. Always divide by the original (starting) value, not the new one. For a percentage decrease, use the same steps with the amount the value dropped. Dividing by the wrong number — the new value instead of the original — is the most common mistake on these items.

How do you solve a ratio or proportion problem?

Write the ratio as a fraction, set it equal to the unknown ratio, and cross-multiply to solve. If 3 operators monitor 9 machines, the ratio is 1 operator to 3 machines; for 45 machines you need 45 divided by 3, or 15 operators. Keep the same quantities on top and bottom of each fraction. A proportion is just two equal ratios, so a / b = c / d means a times d equals b times c. Check that your units line up — operators with machines, gallons with minutes — before you cross-multiply.

How do you plug values into a formula you're given?

Read the formula and the units it expects, substitute each given value in the matching spot, convert units first if they don't match, then do the arithmetic in order (parentheses, multiply and divide, add and subtract). The POSS gives you the formula — your job is a clean, careful substitution, not memorization. One Mathematical Usage version is built entirely around using formulas and conversions provided at the start of the test. Estimate a ballpark answer first so an obviously wrong choice from a unit slip is easy to catch.

How do you find the average speed of something?

Average speed equals total distance divided by total time. A vehicle that covers 120 kilometers in 1.5 hours averages 120 divided by 1.5, or 80 kilometers per hour. The same rate relationship — distance equals rate times time — also lets you solve for distance or time when you know the other two. Match your units before dividing: if time is in minutes but you want km per hour, convert minutes to hours first. Rearrange distance = rate times time as needed: rate = distance / time, and time = distance / rate.

How do you find the next figure in a picture series?

Compare each figure to the next and isolate the single change — a rotation, a reflection, an added or removed element, or a count or size change. Once you name that one rule, apply it again to predict the next figure. If a triangle rotates 90 degrees clockwise each step, just continue the rotation. Figural reasoning items use Picture Series, Picture Comparison, and Picture Progression — all reward finding one consistent rule. If more than one thing seems to change, track each change separately (orientation, then count) and apply both.

How do you track a rotating shape across a sequence?

Pick a reference point on the shape (the tip of an arrow or a marked corner) and step it through the rotation one move at a time. A 90-degree clockwise turn moves up to right, right to down, down to left, and left back to up; four turns of 90 degrees complete a full circle and return the shape to its start. Counting in 90-degree steps keeps you from guessing the final orientation on multi-step items. After four 90-degree clockwise steps the shape is back where it began, so the fifth step matches the first.

What is the difference between rotation and reflection of a figure?

A rotation turns a shape around a center point while keeping it facing the same way around the turn; a reflection flips it across a line to make a mirror image. A rotated letter keeps its handedness; a reflected one is reversed — the classic trap on figure questions is choosing a mirror image when only a turn was applied. Eliminate mirror-image choices first when the rule is a rotation, and turned-but-not-flipped choices when the rule is a reflection. Watch handedness: a reflected figure swaps left and right, while a rotated figure does not.

What does a flywheel do in a machine?

A flywheel is a heavy rotating wheel that stores rotational (kinetic) energy and releases it smoothly. Its inertia resists changes in speed, so it carries an engine through the parts of a cycle that produce no power and evens out the delivery of torque. More mass farther from the center means more energy stored. Flywheels smooth out the pulsing power strokes of an engine so the output shaft turns steadily. The same stored-energy idea lets a flywheel briefly supply extra torque when a load suddenly increases.

Why do bearings reduce friction in machinery?

A bearing replaces sliding contact with rolling contact (balls or rollers) or a thin film of lubricant, so far less surface drags against itself. Less friction means less wear, less heat, and less wasted energy, which lets shafts and wheels turn freely. That's why rotating plant equipment rides on bearings. Rolling friction is much smaller than sliding friction, so ball and roller bearings cut energy loss sharply. Lubrication adds a fluid film that further separates the surfaces and carries heat away.

The Plant Operator Selection System — a battery of four timed aptitude tests from the Edison Electric Institute, used to select candidates for operator jobs in fossil, nuclear, and hydroelectric power plants.

The single combined score, ranging from 0 to 15, that the POSS produces from the four tests; it predicts overall plant-operations effectiveness and is used to rank candidates.

The POSS test that measures your understanding of mechanical principles using pictorial situations, each with three answer choices (A, B, or C).

The POSS test that measures skill with formulas, conversions, algebra, and word problems — solved by hand, without a calculator.

The POSS test that measures your ability to identify patterns among figures, through Picture Series, Picture Comparison, and Picture Progression items.

The Construction and Skilled Trades Selection System — the sibling EEI test for trade jobs. It shares Reading, Math, and Mechanical tests with POSS but uses Graphic Arithmetic instead of POSS's Figural Reasoning.

FREE POSS Study Guide 2026 + Quizzes & Readiness Score

Q: What is the POSS test?

The POSS (Plant Operator Selection System) is a battery of four timed aptitude tests from the Edison Electric Institute (EEI), used by electric utilities to select candidates for operator jobs in fossil, nuclear, and hydroelectric power plants. It covers Reading Comprehension, Mathematical Usage, Mechanical Concepts, and Figural Reasoning.

This free POSS study guide teaches the — the battery of four timed aptitude tests the uses to hire power-plant operators.^[1] The POSS is given for operator jobs in fossil, nuclear, and hydroelectric plants, so it screens for the reading, math, and mechanical reasoning the job demands.^[2]

It’s interactive, not a wall of text: every test has a built-in checkpoint quiz, hover-able glossary terms, worked examples, labeled mechanical diagrams, and concept questions, so you learn by doing.

Work through the four test modules, test yourself at each checkpoint, then round out your free POSS prep with our practice questions and flashcards.

POSS Exam Snapshot

POSS at a glance (2026)
Detail	POSS
What it is	An EEI pre-employment aptitude battery for power-plant operators
Tests	Reading Comprehension · Mathematical Usage · Mechanical Concepts · Figural Reasoning
Reading Comprehension	36 questions, 30 minutes (5 passages)
Mathematical Usage	18 questions / 7 min, or 46 questions / 17 min (one version per battery)
Mechanical Concepts	44 questions, 20 minutes (pictorial, answers A/B/C)
Figural Reasoning	20 questions, 10 minutes
Total time	About two hours to administer (incl. instructions & examples)
Scoring	Number correct (no guessing penalty) → EEI Aptitude Index, 0–15
Passing	No universal pass mark — each utility sets its own cutoff and ranks candidates
Calculator	Not allowed
Publisher	Edison Electric Institute (EEI)

The most important thing to understand is that the POSS is four separate tests, each with its own clock, that combine into one from 0 to 15.^[1] There is no penalty for guessing, so you should answer every question. Because hiring utilities rank candidates by that index, the goal isn’t just to pass — it’s to score as high as you can on all four tests.

What the POSS measures — four timed tests

The EEI Plant Operator Selection System combines four separately-timed tests. Each is scored on its own raw number correct, then the four roll up into a single aptitude index used to rank candidates for power-plant operator jobs.

Reading Comprehension

Read a technical / plant-operations passage
Find the main idea & specific details
Draw conclusions from the text only
Follow multi-step written procedures

Mathematical Usage

Arithmetic, fractions, decimals, percents
Ratios, proportions & unit conversions
Plug numbers into a given formula
Read values off a table or graph

Mechanical Concepts

Simple machines — pulleys, levers, gears
Hydraulics, pressure & fluids
Force, work, friction & motion
Plant equipment: pumps, valves, motors

Figural Reasoning

Spot the rule in a series of figures
Rotation, reflection & pattern changes
Pick the figure that comes next
Find the odd shape out

This guide teaches all four tests as four study modules, in the order that builds fastest: Reading and Mathematical Usage first (the most transferable skills), then Mechanical Concepts (the most content to learn) and Figural Reasoning. The chart below shows roughly how the questions split on the long-form (146-question) battery:

Roughly how the POSS splits its questions (2026, long-form battery)

Mathematical Usage31% · ≈ 46 questions

Mechanical Concepts30% · ≈ 44 questions

Reading Comprehension25% · ≈ 36 questions

Figural Reasoning14% · ≈ 20 questions

Math and Mechanical Concepts are the largest shares on the long-form battery, so weight your study there — but Reading is a big block of points too, and Figural Reasoning is quick to learn once you know the patterns.^[1] The short-form battery uses a smaller, 18-question Math test, but the four test types are always the same.

1 · Reading Comprehension

Reading Comprehension is 36 questions in 30 minutes — five passages, each with several questions.^[1] The passages read like power-plant training and safety manuals, but you never need outside knowledge: every answer is supported somewhere in the text. The three skills below cover almost every reading item.

Main idea & supporting details

The main idea is the single point the whole passage supports; supporting details are the facts, numbers, and steps that prove it. For a main-idea question, choose the option that covers the whole passage — not just one paragraph. For a detail question, scan back to the exact sentence rather than trusting your memory.

Reading question types and how to attack them
Question asks for…	How to answer it
Main idea / best title	Pick the choice that covers the whole passage, not one detail
A specific fact	Scan back to the exact sentence that states it
The meaning of a word	Use the surrounding sentence (context) to define it
An inference / conclusion	Choose what the text supports — never outside knowledge
The purpose of a step	Find why the passage says the step is done

Inferences & drawing conclusions

An inference question asks for something the passage implies but doesn’t state outright. The discipline is to stay inside the text: choose the conclusion the passage supports, and reject any choice that is true in the real world but not backed by these specific words.

Following written procedures

Operator manuals are full of ordered steps and conditional rules (“if X, then do Y”). Reading items often test whether you can follow a procedure exactly: note the order of steps and any conditions that change what to do. Underline sequence words — first, then, before, unless, until — as you read.

Checkpoint · Reading Comprehension

Question 1 of 10

A passage describes a complex system used to purify water involving several chemical and physical processes. Which of the following is a primary purpose of introducing chlorine in the water purification process?

2 · Mathematical Usage

Mathematical Usage tests formulas, conversions, algebra, and word problems — solved by hand, with no calculator.^[1] One battery uses a short 18-question test built around formulas and conversions given at the start; the other uses a 46-question test that adds algebra and word problems. Either way, a clean setup beats heavy computation — the numbers are usually friendly on purpose.

A repeatable routine for Mathematical Usage items

Math Usage rewards a clean setup more than heavy computation. Run this routine on every item until it is automatic — it kills the careless mistakes that cost the most points.

1. Read for the questionUnderline exactly what's asked and the units (gallons? psi? minutes?). The wrong target is the #1 careless error.
2. List the numbers & the formulaWrite down the given values and the relationship — distance = rate × time, P = F ÷ A, part = percent × whole.
3. Match units before you computeConvert so units agree (minutes ↔ hours, inches ↔ feet). Many POSS math items hinge on a unit conversion.
4. Estimate, then solveRound to a ballpark answer first so a wildly-off choice is obvious; then do the clean arithmetic by hand (no calculator).
5. Check the answer against the questionRe-read what was asked and confirm your number answers it, in the right units, before you select.

Formula & unit conversions

On the formula version, the test gives you the formula — your job is a careful substitution. Read what the formula expects, plug each value into the matching spot, convert units so they agree, then compute in order. Unit conversions (minutes ↔ hours, liters ↔ cubic meters) are where most points are won or lost.

Common conversions to have automatic
From	To	Rule
Minutes	Hours	÷ 60
Liters	Cubic meters	÷ 1,000
Feet	Inches	× 12
Fraction	Percent	Divide, then × 100 (¾ = 75%)
Percent	Decimal	÷ 100 (25% = 0.25)

Percentages, ratios & proportions

Percent, ratio, and proportion items are everywhere. For a , divide the change by the original amount and multiply by 100. For a or , set the two ratios equal and cross-multiply.

The math relationships you'll use most
Problem type	Set it up as
Percent of a number	part = percent × whole
Percent change	change ÷ original × 100
Ratio / proportion	a / b = c / d (cross-multiply)
Distance / rate / time	distance = rate × time
Average speed	total distance ÷ total time
Splitting a total	total ÷ number of parts

Word problems & rates

Word problems turn a plant situation into a quick calculation. Translate: name what’s asked, label the numbers, set up the relationship, then solve. Rate problems lean on distance = rate × time and its rearrangements.

Checkpoint · Mathematical Usage

Question 1 of 10

If a cylindrical tank holds 600 liters of water and is filled at a rate of 20 liters per minute, how many minutes does it take to fill a quarter of the tank?

3 · Mechanical Concepts

Mechanical Concepts is 44 pictorial questions in 20 minutes, each showing a mechanical situation with three answers (A, B, or C).^[1] It measures how well you understand mechanical principles — so a handful of rules about simple machines, fluids, and force cover most of the test. This is the most content-heavy module, and the highest-yield place to study.

Pulleys, levers & gears

Simple machines trade force for distance. A ’s equals the number of rope segments supporting the load; a obeys effort × effort-arm = load × load-arm; and meshed gears trade speed for by their .

Pulleys — mechanical advantage = rope segments supporting the load

One of the most-tested mechanical ideas. To find the effort, divide the load by the number of rope segments that support it. More segments = less effort, but more rope to pull.

Fixed pulley

MA = 1

Changes the direction of the force only — pull down to raise a load up. No force is saved.

300 lb load → 300 lb effort

Movable pulley

MA = 2

The load hangs on 2 rope segments, so each carries half. Effort is halved (you pull twice the rope).

300 lb load → 150 lb effort

Block & tackle (4 segments)

MA = 4

Count the rope segments supporting the load — that count is the mechanical advantage.

300 lb load → 75 lb effort

Rule: effort = load ÷ number of supporting rope segments. A machine never gives free work — what you save in force you pay back in distance.

The three classes of lever

Identify a lever by what sits in the middle. Law of the lever: effort × effort-arm = load × load-arm — a longer effort arm multiplies your force.

Class 1 lever

Fulcrum in the middle

Seesaw, crowbar, pliers — can multiply force or just change direction.

Class 2 lever

Load in the middle

Wheelbarrow, bottle opener — always multiplies force (MA > 1).

Class 3 lever

Effort in the middle

Tweezers, a shovel's top hand, your forearm — gains speed/range, not force (MA < 1).

Meshed gears — direction & gear ratio

Two externally meshed gears always turn in opposite directions. The gear with more teeth turns slower but with more force (torque) — exactly how a gear reducer works on plant machinery.

Gear ratio = driven teeth ÷ driver teeth = 30 ÷ 10 = 3 : 1. The driven gear turns at one-third the speed with three times the torque. An idler gear between them flips the direction but does not change the ratio.

Hydraulics, pressure & fluids

questions rest on : pressure in a confined fluid is equal everywhere, and = force ÷ area. So a small force on a small piston makes a large force on a large piston — the force ratio equals the area ratio. works the same way with compressed air.

Hydraulics — a small force makes a big force (Pascal’s principle)

Pressure in a confined fluid is the same everywhere, so a small piston and a large piston share one pressure. The large piston’s greater area turns that pressure into a much larger force.

Input piston

Area = 2 in²

Force = 50 lb

Same pressure

P = F ÷ A

= 50 ÷ 2 = 25 psi

Output piston

Area = 20 in²

Force = 25 × 20 = 500 lb

Force = pressure × area. A 10× bigger output area gives a 10× bigger force (mechanical advantage = A₂ ÷ A₁). This is how hydraulic jacks, presses, and plant actuators work.

Force, work, friction & plant equipment

The rest of the module covers everyday mechanics: work = force × distance, opposing motion (reduced by and lubrication), a storing rotational energy, and balance around a pivot. Expect plant equipment too — pumps, valves, motors, condensers, and belts.

High-yield mechanical facts for the POSS
Concept	What to remember
Pulley effort	Effort = load ÷ number of supporting rope segments
Lever law	Effort × effort-arm = load × load-arm
Gear ratio	Driven teeth ÷ driver teeth; more teeth = slower, more torque
Hydraulic force	Force = pressure × area; same pressure throughout the fluid
Friction & bearings	Bearings/lubrication cut friction, wear, and heat
Flywheel	Stores rotational energy; smooths out power delivery
Belt drive	Over-speeding a belt causes slippage; tension transmits power

Checkpoint · Mechanical Concepts

Question 1 of 10

When a belt-driven machine operates at a higher speed than designed, what is likely to happen to the belt?

4 · Figural Reasoning

Figural Reasoning is 20 questions in 10 minutes, testing whether you can spot a pattern among figures — through Picture Series, Picture Comparison, and Picture Progression items.^[1] It tests reasoning, not knowledge, so practice moves the needle the most: the whole skill is isolating the one rule that changes from figure to figure.

Picture series & progressions

A shows figures that change by a consistent rule; you pick what comes next. Test for the same patterns that drive number series — repeating cycles, a steady count or size change, or a steady rotation — then continue the rule one more step.

Number-series patterns — find the rule, then the next term

Series items reward a fixed routine. Check first for a constant difference (arithmetic), then a constant multiplier (geometric); if neither fits, look for two rules alternating or two sequences woven together.

Arithmetic (add/subtract a constant)

7, 12, 17, 22, …

Rule: +5 each step → next term: 27

Arithmetic (decreasing)

60, 53, 46, 39, …

Rule: −7 each step → next term: 32

Geometric (multiply by a constant)

2, 6, 18, 54, …

Rule: × 3 each step → next term: 162

Alternating (two rules combined)

5, 10, 8, 16, 14, …

Rule: × 2, then − 2, repeat → next term: 28

Interleaved (two woven sequences)

3, 20, 6, 17, 9, 14, …

Rule: odd spots + 3; even spots − 3 → next term: 12

Rotation, reflection & comparison

Most figure changes are a (turning around a center) or a (a mirror flip that reverses left and right). The classic trap is picking a mirror image when only a turn was applied. Track a reference point — an arrow’s tip or a marked corner — one step at a time.

Figural reasoning — the transformations to look for

A figure series changes by one rule from step to step. Find that single change, then apply it to predict the next figure. The most common transformations:

RotationTurn the shape 90° or 180° (an arrow up becomes an arrow right or down).

ReflectionFlip the shape across a line — its mirror image (left becomes right).

Add / remove elementA dot, line, or smaller shape appears or disappears each step.

Count or size changeThe number of items, or the size of the shape, increases or decreases.

Example (rotation, 90° clockwise):↑→↓←

Isolate the one change between consecutive figures, then apply exactly that change again to find what comes next.

Checkpoint · Figural Reasoning

Question 1 of 10

A series of shapes changes from a square to a circle and then to a triangle. If the pattern repeats every three shapes, what will be the seventh shape in the sequence?

How the POSS Is Scored

Each of the four tests is scored on the number of questions you answer correctly, with no penalty for guessing — so never leave a blank.^[1] Those four scores combine into a single from 0 to 15, which predicts how effective you’re likely to be in plant-operations work.

How the POSS is scored

There is no national pass mark. Each test is scored on raw number correct (no penalty for guessing), and the four combine into a single EEI aptitude index used to rank candidates.

Step 1 · Raw scores

Number correct on each of the four tests — no guessing penalty, so answer every item.

Step 2 · Aptitude index

The four raw scores combine into one EEI index that predicts on-the-job success.

Step 3 · Utility cut score

Each hiring utility sets its own cutoff and ranks candidates — a higher index ranks you higher.

Because candidates are ranked, the goal isn’t just to pass — aim for the highest index you can on all four tests, since there is no penalty for guessing.

There is no universal pass mark. Each hiring utility sets its own cutoff and ranks candidates by their index, so a higher score ranks you higher for the job. The practical goal: maximize your number correct on every test, and — because there’s no guessing penalty — make sure you’ve answered every question before time runs out.

How to Use This Study Guide

A study guide is a map, not the whole territory — use it alongside timed practice and our free tools. Because each POSS test is separately timed, pacing is a skill you have to rehearse, not just knowledge to absorb.

A study game plan for the POSS

The POSS rewards both knowledge and speed. Run this loop until each step is automatic, then prove it with full, timed practice.

1. Learn the four tests coldReading, Mathematical Usage, Mechanical Concepts, and Figural Reasoning — know the format and timing of each before test day.
2. Build the mechanical corePulleys, levers, gears, and hydraulics recur the most; learn the rules and the simple formulas behind them.
3. Drill mental math, no calculatorLock in fraction-to-percent conversions, unit conversions, and clean arithmetic — POSS math is by hand.
4. Practice figural series under timeTrain your eye to isolate the single change (rotation, reflection, count) and predict the next figure fast.
5. Rehearse the clockEach test is separately timed, so take full, timed practice runs until your pacing is automatic.
6. Answer everythingThere's no guessing penalty, so never leave a blank — make your best choice on anything you can't finish.

A study loop that actually works

1
Learn the four tests
Work the modules so every format — reading, math, mechanical, and figural — is instantly familiar.
2
Take the checkpoint
The quick check at the end of each module exposes what didn't stick.
3
Drill the gaps
Send your weakest area straight into the free practice questions and flashcards.
4
Rehearse the clock
Take full, timed practice runs so your pacing on each separately-timed test is automatic.

POSS Concept Questions

The kinds of reasoning and mechanical knowledge the POSS actually measures — at least one per test. Tap any card for a short, exam-ready answer backed by an official EEI source, then test yourself on them as flashcards.

POSS Glossary

Quick definitions for the terms you’ll see most across the POSS:

Aptitude Index: The single combined score, ranging from 0 to 15, that the POSS produces from the four tests; it predicts overall plant-operations effectiveness and is used to rank candidates.
Bearing: A component that lets a shaft or wheel turn freely by replacing sliding contact with rolling contact (balls or rollers) or a lubricant film, reducing friction.
CAST: The Construction and Skilled Trades Selection System — the sibling EEI test for trade jobs. It shares Reading, Math, and Mechanical tests with POSS but uses Graphic Arithmetic instead of POSS's Figural Reasoning.
Edison Electric Institute (EEI): The trade association of U.S. investor-owned electric utilities that develops and publishes the POSS, CAST, and related pre-employment selection tests.
Figural Reasoning: The POSS test that measures your ability to identify patterns among figures, through Picture Series, Picture Comparison, and Picture Progression items.
Flywheel: A heavy rotating wheel that stores rotational energy and releases it smoothly, evening out the delivery of power in an engine or machine.
Friction: The resistance force when two surfaces move against each other. Bearings and lubrication reduce it, cutting wear, heat, and wasted energy.
Fulcrum: The fixed pivot point a lever turns on. Where it sits — middle, near the load, or near the effort — defines the three classes of lever.
Gear ratio: Driven-gear teeth divided by driver-gear teeth. A larger ratio means the output turns slower but with more torque; a 3:1 ratio gives one-third the speed and three times the torque.
Hydraulics: The use of a confined liquid to transmit force. By Pascal's principle, the pressure is equal throughout the fluid, so a large piston produces a much larger force than a small one.
Lever: A rigid bar that turns on a fulcrum. Levers obey the law of the lever: effort × effort-arm = load × load-arm, so a longer effort arm multiplies force.
Mathematical Usage: The POSS test that measures skill with formulas, conversions, algebra, and word problems — solved by hand, without a calculator.
Mechanical advantage: How much a machine multiplies your effort — the load divided by the effort. A mechanical advantage of 4 means a 1-pound effort can balance a 4-pound load (at the cost of more distance).
Mechanical Concepts: The POSS test that measures your understanding of mechanical principles using pictorial situations, each with three answer choices (A, B, or C).
Pascal's principle: A change in pressure applied to a confined fluid is transmitted equally throughout it — the basis of hydraulic jacks, presses, and brakes.
Percentage increase: The change divided by the original amount, times 100. Going from 150 to 180 is a change of 30 over 150, or a 20% increase.
Picture series: A figural item showing figures that change by a consistent rule from one to the next; you identify the rule and pick the figure that comes next.
Pneumatics: The use of compressed air or gas to transmit force or do work — similar to hydraulics but with a compressible fluid.
POSS: The Plant Operator Selection System — a battery of four timed aptitude tests from the Edison Electric Institute, used to select candidates for operator jobs in fossil, nuclear, and hydroelectric power plants.
Pressure: Force spread over an area: pressure = force ÷ area, measured in pounds per square inch (psi). The same force on a smaller area makes more pressure.
Proportion: A statement that two ratios are equal (a/b = c/d). Cross-multiplying gives a × d = b × c, which solves for an unknown term.
Pulley: A wheel with a grooved rim that a rope rides in. A fixed pulley only changes the direction of a force; movable pulleys and block-and-tackle systems multiply force by the number of rope segments supporting the load.
Ratio: A comparison of two quantities, such as 3 operators to 9 machines (1:3). Setting two ratios equal makes a proportion you can solve by cross-multiplying.
Reading Comprehension: The POSS test that measures how well you read and understand the kind of material found in power-plant operator training and safety manuals — five passages, each with several questions.
Reflection: Flipping a figure across a line to make a mirror image, which reverses left and right — distinct from a rotation, which does not.
Rotation: Turning a figure around a center point. A 90° clockwise turn moves up→right→down→left; four such turns complete a full circle back to the start.
Torque: A turning or twisting force. Gears, levers, and motors trade speed for torque: slowing rotation down increases the available torque.

Free POSS Study Materials & Resources

Everything you need to prepare for the POSS is free here — no paywall, no sign-up. This guide is the foundation; pair it with the rest of our free POSS study materials for active recall and timed practice:

POSS Practice Test — exam-style questions across all four tests, with explanations.
POSS Flashcards — active-recall decks for the mechanical rules, math conversions, reading strategy, and figural patterns.

POSS Study Guide FAQ

The POSS (Plant Operator Selection System) is a battery of four timed aptitude tests from the Edison Electric Institute (EEI), used by electric utilities to select candidates for operator jobs in fossil, nuclear, and hydroelectric power plants. It covers Reading Comprehension, Mathematical Usage, Mechanical Concepts, and Figural Reasoning.

References

1.Edison Electric Institute. “Plant Operator Selection System (POSS) Testing Brochure.” Edison Electric Institute. ↑
2.Edison Electric Institute. “EEI's Employment Test Batteries.” Edison Electric Institute. ↑
3.Edison Electric Institute. “Plant Operator Selection System (POSS) Testing Brochure (PSEG mirror).” PSEG. ↑

Sources for the concept answers

Every answer in the POSS concept questions above is drawn from an official EEI source:

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