Category: Metrological standards

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

Brick (reference standard) – The object of zero unlonnture (Ǔ = 1.0); the gold standard of staying put.
Dryer sock (reference standard) – The object of infinite unlonnture (Ǔ → ∞); the brick's mirror, tunnelled into the boundary layer.
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.
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 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.
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.
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.