here is a formula that is really quite simple,if the line is at a 15 degree angle multiply the length of the line by 2, if 30 degree multiply by 5, 45 degee multiply by 7, and 60 degree multiply by 8, example 100ft line at 45degree angle to water your fishing at 70 ft move the descmial over one space 30 degree with 100 ft line 100 x 5 =500 (50.0) ft deep knowing how much line you have out is the hard part, doug