Chapter XX

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6. TRADE-UNITS OF WEIGHT

It is unnecessary to describe or even name the various weights peculiar to trade or local custom. Everyone in the trade knows them; out of it no one need know them. If a person not in the trade buys a cask of wine, a barrel of beer, a sack of flour or a load of potatoes, commonsense prompts him to ask how many gallons or pounds are contained in these units. It is the same in France and other countries of the metric system, where the cask, the sack, the churnful, &c., are trade-units with their peculiar equivalents of litres or kilogrammes. It is indeed by the use of trade-units that manufacturers evade the rigour of the metric system.

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