Quote Originally Posted by xpatUSA View Post
Yes, in an old Kodak application note, it says:

"There are two basic types of ISO: saturation-based and noise-based. The saturation-based ISO is also referred to as the ‘base ISO'.

from: kronometric.org/phot/exp/ISOiawKodak.pdf

It's an old Note, the other methods introduced later by ISO (SOS, REI) are not mentioned at all.

Indeed so, Dave. Thus it was that Canon was allowed to reduce the headroom afforded by saturation-based, according to this well-respected Canonista:

Since I posted the above, I've had cause to look at some recent Canon image's EXIF data.

The EXIF "SensitivityType" tag 0x3880 for those images has usually said "Recommended Exposure Index" (REI). That's the one where the manufacturer decides the ISO number that is best for you but based on their tests . . .

. . . pathetic.