Status M vs. Status A transmission density??

Could someone please explain the difference between status M vs. status A transmission density. I'm just starting a new round of testing with my Xrite 820 and can't find any info on this. I did note that Kodak requires Status M when measuring color film. What do you use for B&W film?

Thanks.

If you're measuring color negs, yes, use Status M. For color prints or transparencies, use Status A. The two setups, Status A vs Status M are not drastically different - their sensitivity peaks are roughly 10-20 nm apart in wavelength. Apparently, however, this is significant for the dye sets they are intended to measure.

For B&W, you would generally use the "visual response" setting, but in reality any of the color settings will likely give nearly the same reading.