When I do a reading with the camera for comparison, I either use a gray card or a flat object of uniform color and it's evenly illuminated. I made sure that the gray card fills the frame of the camera and the camera doesn't cast shadow on the card. With a meter like the Minolta Flashmeter III in reflected mode it's difficult to make sure that the card fills its entire view but to compare I have to make sure of that. Doing so my Nikon F5, F3HP, FM, Minolta Flashmeter III, Flashmeter VI, Spotmeter M all read within 1/3 stop. The meters are reading closer to each other than that 1/10 stop.
I actually did this, but I see there is something afoot that I haven't taken into consideration when comparing camera meters to hand held meters.