Meters can vary by over a full stop in the readings they give. Every meter that I've every bought needed to be calibrated. You shoot photos at various exposures and learn how the meter works in relations to the exposures you want to get. With digital, if you have a histogram display, you can use a gray card. Simple shoot at what the meter shows is the correct expousre, a full frame shot of the gray card. Then look at the histogram. For right on exposure, there should be just one spike right in the middle of the histogram and pretty much nothing anywhere else. If the spike is not in the middle, re-expose either up or down till it is.
Cheers,
rfs
