I was sure I posted a thank you several hours ago but I don't see it now.
Anyway, thanks all... that is truly surprising. I've used this scale many times but always wondered about this. I did in fact pull it up in PS and sure enough, the eyedropper measured the same throughout the step. Keith's answer helps get at the "why". And Roy: the thing is, that was a tiff file I put in the Dropbox - go figure!