For the OP - ISO refers to a standards organization and is an accepted set of values that all camera manufacturers, sensor manufacturers, and film manufacturers have adopted, so the value should be a consistent measurement of light, same for film or digital. Film of course has a lower margin for error (1/3 stop latitude for transparency film vs up to 15 stops for a digital sensor).. I use an old hand held Gossen Luna Pro F set to whatever sensitivity the camera sensor is, and ignore the in camera meter entirely much of the time. No problems, and the same meter measured for film for years and years with excellent accuracy.