True trolling Depth?

[GAMBLER]

I have 4 of the same kind of riggers with 400' of cable on each. They are all rigged with the same 12# weights. I run 2 fishfinders with one transducer tipped back to see the balls. They are all different by a foot or two from each other. As for the depth fishfinder vs. rigger counter, it is about 5 - 7' off. Having 2 fishfinders helps considerably. You can put the ball where you are consistantly seeing marks.