Yes, tweaking the hairspring arm would seem to be the way to do it, although, as I say, I would doubt whether 15% would be a significant difference. Apart from the mechanical innaccuracies of the camera when new, there are also the effects of 30/40 years age to consider! If the shutter speeds have all become a bit slower over the years and a slightly high meter needle means you tend to stop down a little more, the two might counter one another to give the right result! Another option that wouldn't even need the top taking off the camera might be to fudge the ASA setting. Probably the only acid test is that of suction and observation, ie suck it and see!
Originally Posted by cao