Melvin:(posted 8285 days ago)I am curious how you determined you were off 15% and not 25 or 50 %?
Usually getting that close is not noticable unless one uses a lab standard densitometer. It can certainly be made up for in printing very easily, as mentioned, by using a grade harder paper or filter and exposure increase.
One of the basics of Black & White exposure is "Do Tests". At the cost of one roll, one can determine the correct development time for a given camera, lens, film developer combo.
The absolute best explanation I have seen is in Fred Picker's "Zone VI Workshop" book. Other books on B&W bsics cover the same stuff.
Cheers