This is an AC Source Analyser, HP6813B 1750VA rated but with the Dual Power Analyser Option 020. Data Sheet here:-
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I'm interested to know what really is the difference between a standard 6813B and one with the Option 020 installed as my investigation so far indicates the A9 output board and an extra A13 V and I sense board, along with a suitable DSP/GPIB board...