Lostyearsago, the monetary pound originally referred to a unit of account rather than a unit of exchange: a Tower pound mass (slightly less than 350 g) of 0.925 fine silver. Coins of that time were mostly silver pennies, 240 to the unit of account, each ideally weighing in at 32 Tower grains (1.45 g or so) of 0.925 Ag. Edward I. in 1300 was the first ruler to break this monetary/mass relationship, coining 243 pennies from this mass rather than 240; successive devaluations reached their nadir in 1551 under Edward VI., who coined 540 pennies from a Troy pound (a bit over 373 g) of 0.250 Ag. The following year, revaluation reforms began; these stabilized under Elizabeth I., who in 1560 had established the 60 shilling (720 pence) footing of a Troy pound of 0.925 Ag; in 1601, this was devalued to 62 shillings (744 pence) per pound mass. This level lasted until after the Napoleonic wars, when the footing became 66 shillings (792 pence), the UK went on the gold standard, and silver coinage lost unlimited legal tender status. The 20th century saw the reduction, and then elimination, of silver from coinage, followed by the elimination of the £ s. d. subdivision in 1971.
I believe that wool was traditionally weighed in stone.