No. 03
Chunking and Mnemonics — How to Group Digits
What makes people who remember more than 7 digits different? The principle of chunking, the experiment that stretched one person's span to 79 digits, and memory techniques that are actually useful.
Chunking means regrouping individual items into meaningful units so there are fewer things to remember. Memorizing 1 7 7 6 0 7 0 4 as eight separate digits is hard, but read as "July 4, 1776" it becomes a single chunk. This is exactly what Miller (1956) meant when he said memory span is limited by the number of chunks, not the amount of information.
The student who remembered 79 digits
Ericsson, Chase and Faloon (1980) had an ordinary college student (called SF in the paper) practice a digit span task, with digits read at one per second, for about 20 months and more than 230 hours. His span, around 7 digits at the start, grew to 79 digits.
The secret was strategy, not a bigger memory. SF, a long-distance runner, recoded groups of 3 to 4 digits as running times (for example, 3492 → "3 minutes 49.2 seconds, near the world record for the mile") and organized those groups into a higher-level structure. The researchers found no evidence that his short-term memory capacity itself had grown; the key was linking the digits to knowledge he already had in long-term memory.
And the skill didn't transfer. His span for consonant letters, measured over the same period, stayed at about 6. What practice built was "the skill of turning digits into running times", not his memory as a whole.
Everyday ways to group digits
- Give it meaning: turn digits into numbers you already know, such as years, birthdays, bus routes or scores. If something like 1776, 911 or 2001 jumps out, it becomes one chunk.
- Group by rhythm: rehearsing with a steady beat, such as 3-3-4 or 3-4-4, keeps the middle digits from getting mixed up. That's also why phone numbers are written this way.
- Look for patterns: noticing steps (2-5-8), odd and even, or symmetry (3-7-3) lets you remember several digits with one rule. The strings on this site deliberately avoid three-in-a-row runs that go up or down by one (1-2-3), so overly easy patterns don't appear.
- Turn digits into sounds: assigning a consonant to each digit to form words (the major system) or placing items along a familiar route (the method of loci) are advanced techniques used in memory competitions. They take a long time to learn.
Is chunking allowed on this test?
Yes. Most people group digits in twos and threes without even noticing. Just remember that it changes what the score means. A score achieved with an active grouping strategy reflects "storage capacity + strategy", and to compare your own results meaningfully you should solve the test in a similar way each time.
A suggested practice routine
- Do a few forward tests with one by one, 1 second to see your usual span.
- From then on, try rehearsing in groups of 3 with a rhythm. In all-at-once mode it's easy to split the groups visually.
- Once your span grows by a digit or two, apply the same strategy to backward span. It's good practice in reversing group by group.
- Keep in mind that what grew is a "digit task skill". For whether it carries over to other memory tasks, see the memory training guide.
Sources: Miller (1956) Psychological Review 63(2):81–97 · Ericsson, Chase & Faloon (1980) Science 208(4448):1181–1182 · Chase & Ericsson (1982) Psychology of Learning and Motivation 16:1–58