I just read this article
He opened his camera bag. In it were two Leica M4's, equipped with 28mm lenses and dozens of rolls of Tri-X. The top of the bag was covered with yellow tabs. He told us he wrote light conditions on the tabs and put them on rolls as he finished them so he would know how to develop them.
I assume it's about contrast, but how would you do this? What would you change with different lighting?