Why we count to 60 seconds, not to 100

The question looks trivial until you try to explain it to a child: why divide the day into sixties, when everything else is tens? The reason is that time was not divided by modern mathematicians but by Babylonian scribes, roughly 4,000 years ago.

Why 60 and not 10

The Babylonians used base 60, inherited from the Sumerians. Sixty has twelve divisors — 2, 3, 4, 5, 6, 10, 12, 15, 20, 30 — which makes simple division possible without fractions. For a merchant splitting a field or a contract, that mattered enormously.

Greek astronomers, notably Hipparchus and Ptolemy, adopted the system for angular calculations and split it into sixty smaller parts. Medieval mechanical clocks inherited the convention, and once it entered clockmaking it became impossible to change.

The modern second is no longer defined by the Earth's rotation, but by 9,192,631,770 oscillations of the caesium atom.