(Jon of the Clue Crew delivers the clue as he weighs some metal on a scale) A French city lends its name to this system of weight used with precious metals, in which 12 ounces equals a pound
Note that 
since this was a 17th-century merchant, he of course used a balance scale to 
weigh ... 2  1 (12, and if some are negative, convert to 1  2) ....