Which is why I limited my comment to negative films.
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I found that my Pentax digital is 1/3 stop on the overexposure side: High values on Velvia 100 and Astia 100F were a tad off. All I did was set the ISO dial on the meter to 125--fixed, and I no longer have to think about compensating for the error.
One full stop underexposed is a pretty large error, especially for transparency films. You could compensate by adjusting the ISO dial, but having the meter calibrated would be the best solution.
--P
I've got two Pentax spot meters, a digital and an analogue. They agree exactly and have for years. It's amazing! Before going out I meter at a spot on the wall that always reads 7 2/3rds eV. It's never varied. If you don't get that kind of consistency, throw yours out and order a new one. They're cheap compared to your other investments and travel costs. If only the rest of life could be so reliable.