10

Base ten is near-universal across unrelated cultures, and the usual explanation is anatomical rather than mathematical. Twelve and sixty divide more conveniently, and both were used for measure while ten was used for counting.

There are 10 millimetres in a centimetre (worldwide, SI). Engineering drawings in metric countries are dimensioned in millimetres almost exclusively, because a whole number of millimetres avoids the decimal point that a centimetre would require.

There are 10 digits in the number system almost every culture settled on. The usual explanation is anatomical rather than mathematical: ten fingers.

There are 10 limbs on a decapod crustacean such as a crab or lobster (decapods).

There are roughly 10 thousand species of bird. About 11,000 in current checklists, and the figure moves as genetic work splits one species into several — an argument about definitions rather than about discovery.

10 is the atomic number of neon. It is chemically inert, and the orange-red glow it gives off under electrical discharge gave neon signs their name — though most modern 'neon' signs use other gases for other colours.

Decimal survives in computing only where humans read the output. Internally almost everything is binary, and the mismatch is why a tenth cannot be represented exactly and why financial software uses decimal types deliberately.

A 10-year anniversary is named for tin in the modern gift lists. Tin in British lists, tin or aluminium in American ones. A decade is a natural milestone; the material is not.

In the history of Sikhism, ten human Gurus led the community in succession, after which authority passed to the scripture itself rather than to an eleventh person.

In the history of Pythagorean philosophy, the tetractys — ten points arranged in a triangle of four rows — was treated as a figure of cosmic order and sworn upon. Attributed to the Pythagorean school from the sixth century BCE. This is genuinely ancient number symbolism, and it is worth distinguishing from modern numerology that claims descent from it: the Pythagoreans assigned qualities to numbers, but the birth-date digit-summing method sold as Pythagorean today is a twentieth-century construction. This is a scholarly account rather than the tradition's own framing.

The modern decimal (base-10) number system used almost worldwide is generally attributed to humans having 10 fingers — the most common physical counting aid across independently developed early number systems.

There are 10 steps on the Mohs scale of mineral hardness (worldwide, mineralogy). Ordinal rather than proportional: diamond at 10 is about four times as hard as corundum at 9, and corundum only twice as hard as topaz at 8. The scale says which scratches which, and nothing more.

There are 10 pins in a frame of ten-pin bowling (worldwide, World Bowling rules). Arranged as a triangle — the fourth triangular number. Ninepins came first and was banned in parts of the United States in the nineteenth century; adding a tenth pin is said to have been the way around the ban.

At the 1976 Montreal Olympics, Romanian gymnast Nadia Comăneci was awarded the first perfect 10 in Olympic gymnastics history — a score so unprecedented the scoreboard, unable to display it, showed 1.00.

In Vaishnava Hinduism, Vishnu is described as taking ten principal avatars, of which the last is still awaited. The list of ten is the most widely used; other texts give twenty-two or an unlimited number, so the count is a convention rather than a doctrine.

Presented as belief or tradition, not as an established fact.