ATSA Number Differences: How the Section Works

In the ATSA's number differences section, single digits from 1 to 9 appear on screen one after another, and for each new digit you type the difference between it and the digit just before it, using the numeric keypad. Candidates describe answers as always positive (the size of the gap, not a subtraction that could go negative) and the pace as fixed by the screen, roughly two seconds per digit. It is a short-term memory and speed task: you hold one number, compare, answer, and immediately let the old number go.

The FAA doesn't publish a description of this section, and the test content belongs to its vendors. What follows is based on candidate reports, which have been broadly consistent since the ATSA launched in 2016, plus public statements about what the ATSA measures. Details such as timing and the number of rounds may vary between test versions.

What the section asks you to do

Candidates variously call this part "the memory game," "differences" or "number differences." A detailed 2016 write-up shared on the pointSixtyFive controller forum, which later posters largely confirmed, describes it like this:

• A digit from 1 to 9 appears and stays on screen for about two seconds.
• A second digit appears. You type the difference between the two on the numeric keypad.
• A third digit appears, and you type the difference between it and the second digit. The chain continues.
• All answers are positive numbers. The same write-up noted that the differences it saw stayed between 1 and 4, although you shouldn't count on that.
• You can't change an answer once it's entered.

Candidate-reported: that 2016 account described eight rounds of about two minutes each. Other descriptions give different counts, and one candidate who tested in 2021 simply said the section "felt like it lasted ages." Expect several blocks and plan to stay sharp to the end.

Pearson VUE's ATSA page describes the test as covering "decision-making ability, spatial awareness, multitasking, and working memory, among others." Of the seven subtests, this is the one that looks most like a pure working-memory task: the information you need is gone from the screen by the time you need it, and it keeps being replaced.

A worked example

This is an original illustration, not a real test item. Suppose the screen shows these digits in order:

Digit shown	Compare with	You type
3	(nothing yet)	no answer
6	3	3
4	6	2
8	4	4
7	8	1
7	7	0 (if a repeat appears)
5	7	2

Notice two traps. At the digit 4, the previous answer was 3 but the previous digit was 6; you compare digits, never answers. And at 4 after 6 the answer is 2, not −2. Candidate reports don't agree on whether repeated digits (a difference of 0) ever appear, so it's worth being ready to type 0 without hesitating.

Why it feels harder than it looks

Subtracting two single digits is trivial. The difficulty comes from three things happening at once:

1. Updating. Each digit is first the "new" number and then, a moment later, the "old" number you compare against. Your memory has to swap roles constantly.
2. Interference. The answer you just typed is also a digit between 0 and 8, and it's sitting in your head right next to the digit you should be remembering. Mixing them up is the classic error.
3. Fixed pace. You can't pause to recover. A single hesitation can make you miss the next digit, and then the chain feels broken.

Techniques that help

Hold only one number

At any moment you need exactly one thing in memory: the most recent digit. As soon as you've typed an answer, deliberately drop everything except the digit on screen. Some people find it helps to "say" the current digit silently when it appears ("six"), then, when the next one arrives, think only "six to four, two."

Don't store your answer

Type the answer and forget it. If you catch yourself checking whether the last answer was right, you're spending the attention you need for the next digit.

Know your keypad blind

Rest your middle finger on the 5 key (most keypads have a raised bump there) and reach from that home position. If you're looking at the keypad, you aren't looking at the screen. Candidate reports say this section uses the numeric keypad, so practice on one if you can; a laptop's top number row builds different habits.

Recover fast from a miss

If you miss a digit, don't try to reconstruct it. Take the digit currently on screen as your new anchor and answer the next one. One missed item costs far less than three items lost while you're still thinking about the first.

Think in gaps, not subtraction

With small single digits it's often quicker to "see" the distance than to subtract: 4 and 8 are "four apart," 7 and 5 are "two apart." Practicing this way also removes the temptation to compute a negative number.

Common mistakes

• Comparing the new digit with your last answer instead of the last digit.
• Typing the new digit itself rather than the difference, usually after a lapse in attention.
• Rushing to answer before the new digit is fully registered, then second-guessing.
• Losing focus in later rounds. The task stays simple but the section is long, and candidates describe it as tiring.
• Practicing only at slow speeds. A 2020 candidate post advised practicing at the fastest setting available so the real pace doesn't feel like a jump.

How to practice

You don't need special software to start: have someone read digits aloud at a steady two-second rhythm, or record yourself doing it, and answer each difference. What a dedicated drill adds is exact timing, a keypad-first layout and a record of where your errors cluster, for example whether you slip on larger gaps or later in a block.

Our Number Differences demo gives you a short timed run with original sequences, and the full practice version adds longer runs and a review of your answers afterward. It's practice for the format, not a copy of the real test, and it can't predict your band. Because the same "hold, update, discard" skill runs through Memory Variables and the math prompts in the ATC Simulation, it's a good section to start with. See pricing for what each plan includes, or read the overview of all seven sections.

A few short, focused sessions spread over a couple of weeks tend to be more useful than one long session the night before. The FAA's own advice for test day is rest, a proper meal and arriving early; that matters for a memory task like this more than most.

Frequently asked questions

Are the answers ever negative in number differences?

Candidate reports say no: you type the size of the gap between the two digits, so 6 followed by 4 is 2. Read the on-screen instructions on test day in case the format has changed.

Do I compare with the previous digit or the first digit?

With the previous digit. Each new digit is compared only with the one shown immediately before it, which makes it a running chain.

What happens if I miss one?

Candidates report that the sequence keeps going regardless. The best recovery is to anchor on the digit now on screen and carry on, rather than trying to work out what you missed.

Is this section scored on speed or accuracy?

The FAA hasn't published how any ATSA section is scored. Because the pace is fixed, accuracy on each item within the time allowed is what you can control, so that's what to train.