I wondered if an APUGer might be able to give me some advice:

A few months ago I bought a macro bellows for my Bronica-SQB. I've used it a couple of times to test it out, and on both occasions got good results by my un-researched technique of spot metering the the subject directly and the ground glass, then averaging the EV result. Does anyone have some tips for more "sure fire" exposure results? I haven't used it (the bellows) for anything critical yet, but would like to soon.