Miller's Law
The average person can only keep 7 (plus or minus 2) items in their working memory.
Read the original on lawsofux.com →
The scenario: redeeming a gift card during checkout. The customer is reading a 16-character code off a physical card and typing it in — a pure working-memory task. Chunking is why phone numbers and credit-card numbers are always written in groups. The “after” input is live — try typing in it.
Checkout — payment
GH7K-P2M9-XQ4W-L8RT. Four chunks of four sit
comfortably inside working memory, exactly like phone and card numbers. And the order summary became five
scannable lines, so each figure is one glance, not a parsing exercise. Try typing in the field.
Checkout — payment
| Ceramic pour-over set (bone white) | $64.00 |
| Sales tax | $5.28 |
| Standard shipping | $6.95 |
| Discount — AUTUMN15 (15%) | −$9.60 |
| Total due today | $66.63 |
🔍 What changed
- One 16-character blur → four chunks of four (
GH7K-P2M9-XQ4W-L8RT), auto-formatted as you type. - Chunking works with working memory, not against it — the same trick behind phone numbers and card numbers.
- Grouping also makes verification possible: you can compare chunk-by-chunk against the physical card and spot exactly where a typo is.
- The run-on order summary became a 5-line table — one fact per line, total visually anchored at the bottom.
- Nothing was removed or simplified away; the same information was just organized into memorable units.
💼 Explaining it to stakeholders
“There's a reason no one prints phone numbers as ten unbroken digits. Our gift-card field asks customers to juggle sixteen characters at once, and every mistype is a support ticket or an abandoned cart at the moment they're trying to give us money. Grouping the code in fours is a tiny frontend change that cuts entry errors and makes the checkout feel effortless.”