Calibrating a light meter.

I just picked up an old Vivitar No.30 for $2.00. It responds to light so I know the cell isn't fried . I plan on testing it against my FM2 and a grey card.
Question: If it's out of wack how can I adjust the meter (no screw)?
Would I simply tune the iso setting until it reads the same as my Nikon for Tri-X ?

Thanks,
Mike

That's how I would do it, and keep notes of various ISO settings.

Try it as well at a variety of light levels. Sometimes, when meters go out of whack, they become non linear. It could happen that it is 1 stop out at EV 4, but 3 stops out at EV 11.

If it is consistently out by the same amount, then you can just dial in the correction.

One further note - experiment with the position of the meter until you get a good appreciation of the angle of acceptance.

IIRC the very first hand meter I ever owned was a Vivitar 30 - I think I traded it in for my Gossen Profisix.

Matt