> There could be two contributions, gain error and offset error

Mike, thanks for the analysis

Presently I'm using 5% carbon resistors that were simply to hand, and
the LM358, so in this first-draft circuit some error could have been
expected. The project is a proof-of-concept demo, which is no excuse
for not doing it properly, but......

I'll get some 1% and a better amp for a revision

As only a resolution of whole degrees is needed, for the time being I
can use the circuit as is, if I don't have time to revise, and compensate
for the extra gain by changing the comparison number used for rounding
in PIC2's s/w. It's there anyway, so no extra code is needed. The more
important reading is at PIC1, and that's correct

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