Antique Electronics and Vintage Solid State

Analysis of DC zero circuit in the HP 3466A DMM

Can someone explain how the DC zero on the HP 3466A works? The manual with the full schematic is on the Keysight web-site:

The first thing to note is that the topology of the input amplifier is non-inverting on the 20 mV and 200 mV ranges, and is switched to inverting on the higher ranges. …

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