There was an ancient weight, the Tron pound, of variable standard, about 20 Scots ounces. But its actual weight appears to have been 9622 grains, which is exactly 20 ounces of the original Arabic ounce = 481·18 grains. This was abolished by the Act of 1618, which ordered ‘that the standards be kept, two firlots by Linlithgow, the stone weight by Lanark, the ell by Edinburgh, and the pint by Stirling, as of old.’
The Lanark stone was 16 lb. of Scots Trois weight. An inscription on the standard still extant states that it was equal to 15 lb. 14 oz. English Troy, that is to the fictive long Troy pound of 7680 grains. The Scots pound, = 7609 grains, was divided into 16 ounces = 475·5 grains, divided into 16 drops.
The stone was blunderingly described (1618) as ‘the French Trois Stone containing sixteen Trois ounces.’ But it had nothing to do with French weight (in which the ounce = 472·12 grains); its standard was of the Dutch Troy (Trooisch) class, coinciding very closely with that of the Amsterdam pound = 7925 grains, the ounce = 476·5 grains.
When the 7600-grains lb. came to England as the standard of the Assize of Bread, it was known as the Scots or Dutch pound.
An Act of James I (1410), ‘That a Stone be made for weighing fifteen Trois pounds and divided into sixteen Scots pounds,’ leads to a suspicion that there was another Scots pound, of Rhineland standard; for 16 pounds or double marks of Cologne are very approximately equal to 15 long Troy pounds of English standard.
Troy oz., 480 grs. × 16/15 = 450 grs. = Tower oz.
One may thus surmise that the royal pound of Scotland, like that of England up to Tudor times, was of Cologne or Tower standard, and was superseded in course of time by the Amsterdam or Scots Trois pound.
That the Boll be divided into 4 Firlots, and contain 29 inches within the boords, and above 27 and an half-inch even over, and in deepness 19 inches; that the Firlot contain in breadth even over 16 inches under and above within the boords, and in deepness 9 inches; that the Firlot contain 2 gallons and a pint, and the Pint to weigh, of the water of Tay 41 ounces or 2 pounds 9 ounces; so the Gallon weighs 20 pounds 8 ounces, the Firlot 41 pounds and the Boll 164 pounds.