Rule II.: As the Weight of pure Gold in the Guinea, is to the Value of the Guinea in England, so is the Weight of pure G

The Quantity of pure Gold in any Piece is had, by knowing the Weight of the Piece, and the Weight of Allay in a given Weight of the Gold, out of which that Piece is made: for Instance, in the Standard Gold of England, a Pound Weight, or 24 Carrats, contains 22 Carrats of fine Gold, and the same Weight of Portugal Gold, from the Column of Assays in the Table, being a Quarter of a Carrat Grain, or the .0625 Part of a Carrat, better in a Pound than English Gold, will contain 22,0625 Carrats of fine Gold. Then, as 24 is to 22, so is 129.438 Grains, the Weight of the Guinea, to its Weight of fine Gold; and as 24 is to 22.0625, so is 166 Grains the Weight of the Moydore, to its Weight of fine Gold. The Weight of fine Gold in the Guinea will therefore be and the Weight of fine Gold in the Moydore will be and rejecting the common Denominator, will be expressed by 22 × 129 .438, and 22 .0625 × 166.

Then as 22 × 129 .438 is to 21 Shillings, the Value of the Guinea, so is 22.0625 × 166 to the Value of the Moydore in England, which Value is therefore equal to that is, equal to 27.04 Shillings.