The correct answer is actually  ‘Weighing silver and gold used 12 ounces for one pound’.

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There were 20 shillings in a pound (12 pennies in a shilling), 36 inches in a yard (12 inches in a foot), and 12 ounces in a Troy pound used for measuring gold. In Britain, duodecimal measurement (i.e. counting in twelves) was preferred to decimal measurement until the late 20th century, because there are more ways to divide 12 into equal whole numbers than 10.