Hello, until now, nobody has ever reenginered the 732B schematics. Perhaps the bbs.38hot colleagues (lymex et. al.) have done that, but I do not get access to the forum for downloading anything, either. But on eevblog, the Datron 4910 reference element has been decrypted completely, as now the content of the Vishay resistor array is known. Yep, I have to admit, that I also have made much more effort there than here lately. See 'Ultra precision reference LTZ1000'. Anyhow, in the 732B manual, there is that circuit block diagram, showing the usual reference amplifier circuitry. Fluke added some current cancellation circuitry compared to the 732A, and has put all temperature sensitive components inside the oven. That includes especially the 4-5 precision wirewound resistors around the ref. amp., which cause the most drift over temperature and time. I think that's all with 732Bs magic. The 732B had two series, one earlier with the SZA263 (Motorola) and after termination of that part, a compatible 2nd source from LT, the LTFLU refence amplifier. The mentioned Fluke / Deaver document analyses the different drift behaviour of those two components, but in general, the 732A (based on the SZA263) was less stable, afaik. Frank