Number memory

The game measures your digit span: how long a number you can hold for a few seconds and repeat exactly. It's one of the oldest measures in memory research, and people typically manage around seven digits in classic tests. Going well past that usually depends on grouping the digits into chunks.

Our version differs from the classic test in one big way: you see the whole number at once instead of hearing it digit by digit, which makes grouping easier.

• Level 1 shows a 3-digit number for 2.2 seconds, with a bar showing the time left.
• Every level adds one digit and about two-thirds of a second, so a longer number also stays up longer.
• When the number disappears, type it back and press Check.
• One mistake ends the run, and the game shows you the number you were trying to remember.
• Your score is the longest number you got right, in digits. The game goes up to 22 digits.
• If you switch apps or tabs while the number is showing, the level replays with a new number and you lose nothing.

• Split the number into groups of three or four as soon as you see it.
• Give a group a meaning where you can: a year, a time, a price, or part of a number you already know.
• Repeat the groups to yourself in a steady rhythm until you start typing.
• Use the whole display time. As the number grows, so does the time you have to group it.