Quote Originally Posted by Tom1956 View Post
Put in 357's, and make a little doughnut spacer out of a strip of paper and some white glue. Set your meter to 1/3 stop higher ASA for starters. The 357 was the only battery to give 50% or greater flat output curve comparison to the 625. Do not use modern 625 alkalines. Their discharge curve is horrendous. You never pin down an ASA on them.
Correction: set to 1/3 stop lower ASA when 357 is new. Set to box speed after 2 months average use. From then on the battery holds flat until falling off a cliff after 1/2 the expected original lifetime of the mercury PX625. Keep this in mind and you wont be fishing in the dark for a film speed. Batteries tend toward the underexposure side when new, and over exposure as they age. The PX625 mercury could hold flat all its life. Silver is a fair to middling runner-up to mercury. The other technologies are no better than alkaline on that count, which is unfit for meter use.