Not wanting to damage my actual scales I decided to risk my cheap but incredibly useful callipers at 1.88v. On the up side I know the meter I was using reads about 0.03v over actual, on the down side 1.85v is still around 20% above the voltage of typical fresh SR44 type battery . I'd normally consider 10% over to be a maximum safe(-ish) voltage but so far so good , I have the PC app working and I've set the scale to -6.66mm for luck. I'll leave it running for a couple of days and see how it goes.

Thanks again Bill, elegant circuit and nicely crafted software