Numbers & Differences

A rolling mental-math and working-memory task: keep the last number in mind and enter the difference as each new number appears.

What it measures

This section tests short-term memory and fast mental subtraction under time pressure. It is the first of the seven reported sections and uses the numeric keypad.

Reported format

A single digit appears, then is replaced by another. You enter the difference between the current digit and the one shown immediately before it.
The reference is always the previous displayed digit, not your previous answer. This is the most common place people trip.
Differences are positive, so the answer is the absolute difference. With single digits the answers fall between 0 and 8.
Candidate reports describe roughly eight timed rounds. The exact round length is debated (commonly cited as 90 seconds, sometimes 120).

Disputed or unconfirmed

Exact round count and round length.
On-screen styling, fonts, and the precise display timing of the opening digit.

How to practice

Anchor on the number currently on screen, compute the gap to the next one, key it, and immediately re-anchor on the new number. Do not let your own answer become the reference. Build speed only after the re-anchoring habit is automatic, because a single wrong reference cascades through the rest of the round.

How this tool handles it

The answer key is the absolute difference against the previous displayed digit, which is the genuine trap rather than a simplification of it.
Round length and count are adjustable so you can practice both the 90-second and 120-second profiles rather than betting on one.

Practice this section All guides

Sources

Pearson VUE (FAA ATSA page). Administration vendor. Source for the 2-hour-49-minute active ceiling plus up to 30 minutes of breaks, the three-year result validity, invitation-only access, the three result categories, and the FAA's statement that it endorses no practice test.
DOT Office of Inspector General, report AV2023011 (Jan 2023). Reviewed how the FAA developed and validated the ATSA, including the selection of 7 of 15 candidate assessments and the use of scoring bands.
U.S. GAO report on the ATSA (2026). Reported that the FAA plans a new version of the ATSA and examined validation of the skills assessment.
FAA hiring-reform announcements (2024-2025). Streamlined the controller hiring process, raised FAA Academy pay, prioritized higher scorers, and removed the earlier biographical assessment.
Candidate and preparation-community reports. First-hand descriptions of task mechanics. Useful for format but unofficial and sometimes inconsistent.

Candidate reports are first-hand but unofficial and can conflict. Where sources disagree, the disputed item is left configurable in the matching practice module rather than fixed to one guess.