Very useful tool to trace the p/n junction curves. Very useful to isolate, open, shorted and more especially those diffcult to find lazy transistors and diodes, matching two or more transistors etc. Usually called curve tracer. But you can do same with your scope using home made ocputus box which I don't know the schematic for, my coworker has that little box but he doesn't know where this schematic of this because he made that curve tracer box decades ago. Cheers, Wizard