Category: Metrology

A top-level category of Obscuripedia. The list below is believed complete, though membership – like everything here – is subject to revision.

• The age of the Earth – Kelvin cooled the planet from first principles and got twenty-four million years. His own former assistant had the right answer in 1895, and let it go.
• Cornelis Baak – Dutch metrologist (1838–1911) who held that a dispute lasts only until the disputed quantity is measured finely enough, and built three instruments that proved it did not.
• Brick (reference standard) – The object of zero unlonnture (Ǔ = 1.0); the gold standard of staying put.
• Celestial navigation – One sight does not say where you are. It says you are somewhere on a circle three thousand miles across, and the craft is everything after that.
• Constant of stubbornness – Proposed fundamental constant (s) underpinning the brick – defined, named, and never measured.
• 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.
• Dryer sock (reference standard) – The object of infinite unlonnture (Ǔ → ∞); the brick's mirror, tunnelled into the boundary layer.
• GPS – The most thoroughly relativistic machine in ordinary civilian use, whose clocks were detuned before launch, and which is regularly offered as evidence that relativity is unnecessary.
• Gravity – The weakest of the four forces and the worst-measured quantity in physics: sixteen laboratories have determined its constant and they do not agree.
• Hairy ball theorem – There is no way to comb a sphere flat, and the reason is a single number. Odd-dimensional spheres comb perfectly, which is the half nobody mentions.
• 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.
• The longitude problem – Not a question about where you are but about what time it is somewhere else. It was solved twice, by two methods that went to sea together for a century.
• Nevil Maskelyne – Fifth Astronomer Royal, remembered as the man who cheated John Harrison. He ran the trial in question, and it beat his own method by three to one.
• The Millikan creep – Millikan's charge of the electron was 0.6 per cent low, and every value published after it climbed towards the truth by small steps for decades.
• The Nautical Almanac – Published every year since 1767, and the reason longitude starts at Greenwich. Every figure in it was computed twice, by two men forbidden to confer.
• 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.
• The Sagnac effect – The fringe shift from sending light both ways round a rotating loop, offered as the disproof of relativity, and in fact a direct measurement of the relativity of simultaneity.
• The speed of light – Measured for three centuries, wrong by four times its own error bar for twenty years, then fixed by vote in 1983. It can no longer be measured.
• 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…
• 30 February 1712 – The only 30 February known to have occurred. Sweden converted to the Gregorian calendar gradually, lost track during a war, and got out by adding a day.
• 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.
• Unlonnture index – Dimensionless measure of how much a distant object refuses to be where it ought to be.
• 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.
• Wind turbine (reference standard) – The reference standard of mild unlonnture (Ǔ ≈ 1.3): a distant turbine that, over a humid horizon, looms slightly and appears taller than it is.

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