Quote Originally Posted by jernejk View Post
One more question: when properly developed and printed, should the gray card on paper be 18% grey, the same as the real grey card? My guess is not, as we are only reproducing the relationships of tones in the scene on a medium that has a shorter tonal scale.

my printed grey card is about a stop brighter than the real thing:
Attachment 79291
A reference point like the grey card provides a connection between scene and print, it is just a place to start, a way to waste less paper when printing. I do use reference points (various and sundry reference points, see below) with my enlarger meter to set exposure for the first print (when I use a grey card) and depending on the target to set paper grade (where there are both a black and a white point).

What a single point does well is to "correct" enlarger exposure for changes in camera exposure (purposeful or inadvertent). This is possible because most negative films have some latitude. This may be why you see little difference between prints from differing EI's with PanF and Delta 100.

(Side note. As reference points I use; my palm, my camera bag, my truck provides both black and white points, asphalt, northern sky, grass, in studio setups I use a rag doll ... Any "known" reference point can work.)