Depth 1 · 37 s

Your foot, my foot

Name: Your foot, my foot
Uploaded: 2026-11-02T18:05:18.972443Z
Duration: 37 s
Description: The same room is 12 of a child's feet long and 9 of an adult's. Both counts are honest, but they don't agree - so people agreed on one length everyone uses, a unit, checked against a standard. And a measurement needs both its parts, a number and a unit.

The same room is 12 of a child's feet long and 9 of an adult's. Both counts are honest, but they don't agree - so people agreed on one length everyone uses, a unit, checked against a standard. And a measurement needs both its parts, a number and a unit.

About this video

How long is a room? A child who walks it heel to toe counts 12 feet; an adult counts 9. Both counted honestly, yet they disagree, because their feet are different lengths. Measuring with parts of the body only works when everyone uses the same body.

The answer people found is a unit: one agreed length that everybody measures with. In ancient Egypt the royal cubit, about 52 cm, was kept as a master rod and copied onto measuring rods for builders, a standard anyone could check theirs against. This short animation shows why that matters, and why a measurement always has two parts. "The room is 4" means nothing until you say 4 what: 4 cubits.

This video shows depth 1 of Units.

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Transcript

0:00How long is this room? Let's walk it, heel to toe.
0:04A child walks it heel to toe: 12 feet.
0:08An adult does the same: only 9 feet.
0:12Both counted honestly, but they don't agree.
0:17The fix: everyone uses one agreed length. That is a unit.
0:21Egypt used the royal cubit, copied onto rods: a standard.
0:25Now someone says: the room is 4. Four what?
0:28A measurement needs both: a number and a unit.
0:32Not your foot or mine. One unit for everyone.