<P> Common in France, where it is called a bouchon doseur boule, this device consists of a transparent T - shaped glass tube arrangement, with a ball on one end of the horizontal section, a cap or cork on the other end, and a cork or plastic bottle stopper on the bottom of the T, allowing the measure to replace the cap of a liquor bottle . In use, the bottle is inverted until the ball fills with liquor, and then tilted in the other direction to let the liquor pour out the spout in a manner that keeps additional liquor entering the measure from the bottle . A promotional video available on YouTube includes a cutaway rendered animation beginning at 2: 15 that demonstrates the 3 - ball mechanical arrangement . </P> <P> The Weights and Measures Act of 1963 made it illegal in Britain for businesses to give short weights or short measures to consumers . Before this there was no legislation, only guidelines as to the correct weight of an alcoholic spirit measure, and if spirit measures or optics were used, they required a government stamp to certify that the measure was accurate . </P> <P> The 1963 Act formalized the legal measures by which spirits and other alcoholic beverages should be dispensed, namely 1 / 4 gill (35.5 ml), 1 / 5 gill (28.4 ml) or 1 / 6 gill (23.7 ml), but this was replaced in 1985 by 25ml and 35ml for single measures, with double measures of 50ml or 70ml being permitted in 2001 . Landlords have the option to decide which quantities they sell, with the difference being caused by historically larger measures being used in Scotland and Northern Ireland . </P> <P> Thimble measures are also used in 175ml and 250ml volumes for measuring wine . Although government stamped for the correct volume, the thimble measure does rely on the user measuring the wine out manually into the thimble . </P>

How much is a single measure of spirit