David, I have as many as 6 different manuals for the 332/335 A/B/Ds. I recommend this one, from 1978, which covers most of he different revisisons of the instruments, in best quality: http://assets.fluke.com/manuals/335d____imeng0100.pdf You have to find out, which chopper, reference, and sample string versions you have. The rest most probably is identical, apart from the additional differential amplifier of the 335, of course. Would you mind describing in detail these 3 circuits of your instrument, please? Frank