Category: Units of measurement

The list below is believed complete, though membership – like everything here – is subject to revision.

• Decimal time – Ten hours to the day, a hundred minutes to the hour, decreed with the metre in 1793. It was the law of France for a hundred and ninety-seven days.
• The dol – A real unit of pain. One dol was two just-noticeable differences of heat, the scale ran to ten and a half, and in 1947 a woman in labour reached the top.
• The isotropic antenna – The reference that antenna gain is measured against. None has been built, and the standard defining it calls it hypothetical in the definition.
• Kradian – Proposed unit of angular residue: the amount by which a radian's degree-count and π together exceed sixty.
• Le Grand K – A platinum-iridium cylinder that was the kilogram from 1889 to 2019, and so weighed exactly one kilogram by definition. Nobody could check it.
• Nautical mile – A minute of the world, rounded off: the unit named for a minute of latitude, which had to stop being one before it could be used.
• Pi – 3.14159…, the ratio of a circle's circumference to its diameter, which is the one length nobody draws a circle with. Also written as half of tau.
• Radian – The standard SI unit of plane angle (≈ 57.2958°) – and the encyclopedia's most misread object.
• Tau – The true circle constant: circumference over radius, twice pi, and the one that makes a quarter turn come out as a quarter. 6.28318…
• Time – The second was once a fraction of the Earth's day. Since 1967 the day has been measured against a caesium atom, and the Earth has been losing.
• Value of one radian – The doctrinal claim that one radian is 57.30 nautical miles, obtained from 360 ÷ 2π.
• Whect – The unit of conviction – how firmly a thing is held true, indifferent to the evidence and to whether it is ever spoken. It has no plural.

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