[wiltw]

I base my information on tests done by the technical staff of Professional Photographer Magazine with a Minolta Autometer VF done in an article in the last few years, this is also why you can programme the sensitivity of Sekonic L-758 Meters to the actual individual sensor of up to four different digital cameras, because they are all have different responses to light. Watch this , and you will understand.
http://www.youtube.com/watch?v=tdyosItw3Mk

Consider also this fact...I happen to have three brands of film cameras, and I get different readings from the meters of each of them pointed at the same 18% grey card. So which would you believe when loaded with a so-called ISO 100 film?! The same issue happens with dSLRs, too. Thge same happens with light meters, too.

We know that the ISO standard equations for incident meters and for reflected meters both have VARIABLE value 'constants', where the manufacturer of the camera/meter gets to choose the value that they use!