if you don't have a depth chart you can do this, look at the angle of your line if it's 45 degrees use a multiplier of .7, .5 for 30 and .25 for 15 degrees. so 50 feet of line at an angle of 45 would be 35 feet deep, 25 for 30 degrees and 12.5 feet for 15 degrees. This works well with dipseys and heavy weights. If you are flat lining cranks it's not as accurate because the line will have a bow in it.