Hi!
All you have to do is download the "FG-CoreRPG-Coins-Weight-Custom-Denominations.ext" file attached to the first post of this thread.
Extract it (it's a zip file) to a folder with the same name and move it to your FG extensions directory.
Open the folder and the scripts subfolder and then open customcoinweightdenominations.lua (it's a text file).
In the section starting with "elseif sRuleset == "5E" then" you should add new lines for each custom currency. Such as:
CoinsWeight.aDenominations['brass'] = { ['nValue'] = 10, ['nWeight'] = .02 }
the number after nValue is how many gp that denomination is worth. the number after nWeight is how many pounds each coin weighs.
When you're done, save the file and load both extensions (coin weight and coin weight custom denominations) in FG.

