SI - system Internationale - a standardised international metric  
system. FPS - feet and pounds
I am always amused when a US retiree (there are quite a few here in  
Queensland) during a medical consultation asks when how many stones  
and pounds they weight after I have given it in kilos. Stones? you  
measure weight in rocks?
Back to harpsichord content, Wil Smith would have measured his wire  
with a slip gauge surely.  Was brass music wire made in England?
I would be interested to hear if anyone has done metrical analysis of  
early English harpsichords like Grant Obrien has done with the  
Italian harpsichords. It might give some clues to the origins and  
associations of these makers with makers on the Continent.