Spotting a digit hidden among letters
These puzzles rely on a simple fact: in most fonts, several letters and digits are nearly identical. A string like O O 0 O O contains one digit — you just have to find it.
The look-alike pairs
Oand0— the classic; a digit 0 is usually narrowerI,land1— serif fonts add a base stroke to 1Sand5Band8Zand2Gand6qand9
How the game makes it harder
Two things change with level: the string gets longer (6 → 9 → 12 → 15 characters) and the filler letters are randomised, so you cannot learn “the digit is always third”.
Scanning technique
Group in threes
Chunk the string into groups of three as you read. Chunking reduces working-memory load — you compare three items instead of fifteen.
Look at the baseline, not the body
Digit 0 is narrower than letter O; digit 1 has a different base; 5 has a flat top bar. Compare the vertical strokes and the baseline rather than the overall silhouette.
Trust the pop-out
If one character seems to “stick out” while you scan, check it immediately. Peripheral vision is good at detecting stroke differences even when you cannot yet name them.
Why this trains anything
This is a discrimination task — the same skill used when proofreading numbers in spreadsheets, checking serial numbers, or reading small print on labels. Fast, reliable discrimination is trainable, and short daily sessions work better than long ones.