// Free practice · Army
Free ACT Error Detection test
Twenty Error Detection questions against the clock, in the format of the British Army Cognitive Test. The original and the copy disappear before you answer – just like the real thing.
- 20 questions
- 2.5 minutes
- Timed
What Error Detection looks like
In the Error Detection section you see two short strings – an original and a copy – for a moment. Then both disappear and you say how many characters were different: 0, 1, 2, 3 or 4 (Mindmill practice booklet). The strings are names, times, reference codes or random characters, so you cannot rely on meaning.
The British Army says the test measures speed and accuracy (British Army). Two habits help: compare in small chunks of three or four characters, and keep a running count rather than trying to remember every change.
How this free test is set up
Twenty questions, two and a half minutes – the same pace as our practice timing of 40 questions in 5 minutes. The Army does not publish question numbers or time limits; our timings come from widely used practice material and may differ from the real test.
This free test is being built.
Meanwhile, try the sample questions on the course page.
No sign-up, no e-mail. Original questions written in the format of the real test, with an explanation for every answer. Updated 23 October 2026.
More free practice
- Want all five sections in one go? Sit the free ACT mini mock test.
- For timed practice of every section and three full mock tests, see the Army Cognitive Test practice course.
- Preparing for a different service? Try the Defence Aptitude Assessment (DAA) sample questions.
- Preparing for a different service? Try the SIA Door Supervisor sample questions.