Let me help. <evil grin>
Croubie - you beat me to the punch! I was writing this when you posted. Great minds think alike. Then again, so do insane ones.
The problem tends to be what your metering when using any form of reflected light meter.
different meters can all give you results that vary by a stop or more - and every one is possibly correct - or every one is potentially off. What you REALLY want to know, is how much light is falling on the subject, and that is done with an incident meter , or metering off a grey card. They should all be fairly close if you use a grey card - if not then one or more of them need calibration. Reflected, you have to engage brain and adjust for where you want to place the value you just metered. ( if spot metering ) or know the charactaristics of how it "sees" the scene. Is it center weighted, averaging, Matrix, etc.
But the meter is only the beginning of your woes.
You have metered, and now you have some numbers to work with, say, f8 @ 250th. But is that f8 REALLY f8? How do you know? And what about the shutter speed. Been calibrated lately, and do you know the true speed? And how about how leaf shutters change relative speed and exposure depending on aperture and shutter speed.
Its enough to drive you bonkers. - So - forget all that, and do the next best thing. TEST. It will save your sanity - or failing that, will give a crazy person some pretty good exposures.
See - the numbers are just funny shaped marks that out brains read as f8, or 1/250th. They are an approximation of what it should be. If the errors on a meter lean slightly to the underexposure side, and the ones on the camera ( shutter actually 1/187th or some such ) tends to give a bit of overexposure - and don't forget that the f stop could be a another 1/3 or more from the actual transmission value. The focal ratio is based on the size of the hole relative to the focal length, not on how much light actually gets through the maze of haze inside the 14 element poorly coated cheap zoom lens, vs. how much gets through your 4 element late coated perfect zeiss tessar - both can be set to f16, but the tessar could pass 2-3X the light to the film.
So if meter tends to underexpose and equipment tends to over expose about the same amount, things cancel each other out and you may have near perfect. Or, they could add up and really screw you up with very underexposed or overexposed results.
Well... at least we now have a LATENT image. Then your development process can have almost as much fun... Thermometer calibration, ph of water used to mix developer, age, oxidation or contamination of developer, etc. Oh, how about your timer, and agitation style. ( Lost all hope yet? )
Fortunate for use, there is a bit of latitude in most films. Amazing we get anything with this madness.
The only really useful answer is test. Bracket and test some more. Of course you could get your shutters all calibrated and adjusted and such. Or just test each lens that has a built in shutter - against a standard negative. Helps to have a densitometer. You know, yet another meter that needs to be calibrated against a known standard... Look! Here come the men in the white suits with the big net.
Now that I have put your mind at ease as to which meter to use, Sleep well.
Blaine
ps. Don't forget that the batteries we use tend to vary in voltage over time, which can also affect results.