Hello,
the sensitivity of built in selenium cell exposure meter is dependent on their size. The cell in the knob is not very large in area and therefore the sensitivity should be lower than with hand-held selenium meters. From my experience with the well known Sixtomat X3 from Gossen, I can say that you can measure all you can shoot hand-held and even a little bit more. The Hasselblad meter is more or less an emergency instrument. Most users prefer an hand-held meter with the possibility of incident light measurement or even a spotmeter acc. to the zone system.