OMG, making it way too complicated. Schotkey diode 1N-6263 in series with the battery. Meter accurate and linear within 1/8th of a stop (after calibration) and since most are shooting print film these days, that "inaccuracy" easily falls within the plus or minus 1.5 stop (or more) latitude of the film. Then there's shutter speed latitude, film asa latitude, f stop latitude, the joker making minimum wage at the drug store pushing the "start" button on the "automatic" machine developing your film. John