Number Memory

Chunk it like a phone number

Nobody remembers 8394712 as seven separate digits. They remember it as 839, 471, 2: a few small groups instead of one long string. That is the entire trick to Number Memory. As the number flashes, break it into chunks of three or four and rehearse the chunks, not the individual digits. It is exactly how you hold a phone number in your head long enough to dial it, and it is the only reliable way to push past the wall most people hit.

Where the wall is

That wall tends to sit around seven digits. Psychologist George Miller named the effect in a famous 1956 paper, The Magical Number Seven, Plus or Minus Two: short-term memory holds about seven items, give or take a couple, and you will feel it right where the number outgrows a single glance. Two things help you climb past it. Say the digits under your breath as they appear, so you are storing a sound as well as a picture; the spoken loop is often more durable than the visual one. And when the number is gone and you are typing it back, replay your chunks in order rather than groping for stray digits.

• Group the digits into threes or fours the instant they appear.
• Subvocalise: quietly say them to yourself to lay down a second memory trace.
• Type back chunk by chunk, in order, rather than digit by scattered digit.

Borrow the tricks of memory athletes

Chunking has a ceiling if your chunks are only sounds. The people who recite hundreds of digits give every chunk a meaning. The classic case is a college runner known in the research as S.F., who trained with psychologists at Carnegie Mellon in a famous study published in 1980. He heard 3492 as 3 minutes 49.2 seconds, close to a record mile, and stored digit groups as running times. After about 230 hours of practice his span went from a normal seven digits to 79. His raw memory never improved; his packaging did. You can borrow the cheap version. Turn chunks into years, prices, ages or jersey numbers: 1945 is the end of the war, 2010 is a birth year, 23 is a famous shirt. A group with a meaning sticks far better than a group that is only noise. Serious memory athletes go further with the Major system, which turns each digit into a consonant sound and each chunk into a word, so 32 becomes moon. You don't need that here, but it shows where the road leads: the record holders aren't really remembering numbers at all. They're remembering stories built from them.

Playing the seconds you're given

The number stays on screen for a few moments, and how you spend them decides the round. Don't read the whole string over and over from left to right; that rehearses the act of reading, not the number. Split it into chunks on first sight, say each chunk once, then spend any spare time repeating the middle chunks, because the middle is what fades. The start and the end of a list look after themselves; psychologists call it the serial position effect, and you can feel it the first time you drop digit six of ten. When the number vanishes, type immediately and in order, chunk by chunk. Keep the inner voice running while your fingers work, because typing the first group is exactly when the last group likes to evaporate. And type carefully: a mistyped digit ends the run just as surely as a forgotten one.

A brain test, not a party trick

Number Memory belongs to a family of quick browser benchmarks that grew popular for measuring one narrow slice of cognition. This one is a clean test of digit span, the classic measure of verbal short-term memory that clinicians have used for over a century; a version of it still sits inside the Wechsler intelligence tests. Each round the number grows by one digit, so the game is really asking how far you can stretch that span before it snaps. Get it right and it hands you a longer number; get it wrong and it tells you the level you reached. Most people land somewhere in single digits. Cracking into the low teens takes real chunking discipline.