[benjiboy]

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!

I basically agree with you from my experience, but since different makes of cameras exposure systems have different parameters in their design it's quite possible to to have some small deviation in their responses when pointed at a Grey Card, I have noticed this myself in my cameras, but I don't find this in practice significant because in isolation each camera gives me correct exposure, and comparing light meter and thermometer readings I find is a very quick way to drive yourself crazy