The Olympus OM-1 has a needle, too, which one centers in a permanently positioned scale. Its needle swings to one side when power is off. I have conducted direct test of Mercury Oxide vs. alkaline, and have found that the amount of error depends not only upon the actual voltage of the alkaline cell (which varies throughout its lifetime), but is also dependent upon the levels of light being metered, so it is impossible to compensate simply.
Originally Posted by monochromeimages
I have heard that if a meter needle is centered in a permanently positioned scale AND its meter needle stays centered when power is off, it uses a Wheatstone bridge circuit and is not subject to devialtions caused by different voltage (alkaline cell).