I just got a totally dead 8842A. After I repair it, I was thinking of perhaps using it as the basis of a homemade 10 VDC reference. It has one of those Motorola buried zener references in it. There is a test point for the 7 VDC reference. I'll have to look at the schematics for the 731 to see how Fluke did things. Joe Gray W5JG