ok its the other way from what i said but you still have same problem of getting a pot with enough resolution, for example one of those multi turn pots with the scales on is best but they cost£££ without it your going to have to use a DMM in wich case you dont actually need the circuit! i like the idea of building a constant current source tho and using that, maybe one those variable voltage regs used as constant current config (not sure if they will go high enough). if its just a fun build thing then fair enough but if its a need it kind of tool there must be better designs on the net?? i am not taking the P by the way just trying to help i am not always good at coming across properly on the net! i never mean anything in a nasty way tho i only ever want to help in my own limited way and learn as i do it