What! The Ell? [Basic Metrology]

Not so long ago just about every trade and occupation evolved a set of units peculiar to itself. Take brewers and tavern keepers for example. Their need to measure liquid volumes, both in bulk and to serve to individual thirsty customers, led to the Tun which equalled two Butts, each being two Hogsheads. Then the very convenient binary sequence is interrupted, a Hogshead being only one-and-a-half Barrels, and resumed with a Barrel being two Firkins which is two Pins and brings us to familiar territory, a Pin being two Gallons, a Gallon four Quarts and a Quart two Pints. At last the thirsty customer gets served. There is further subdivision into Gills, Drams, and Nips for stronger wines and spirits, but beer and ale stop with the pint on the grounds that a lesser quantity than a pint is not worth the trouble of drinking. These antique measures have succumbed to the needs for legal definition in more recent times by declaring the gallon to equal 282 cubic inches. Hence, it is linked to the Systeme International des Unites (SI) since an inch is defined as exactly 25.4 millimetres. That definition of the gallon applies to the U.K., but Americans have been giving short measure with their smaller gallon for centuries.