Absolutely, and you should, since most other methods of determining depth are misleading and do not account for blowback properly.
The line counter on your downrigger reel shows the amount of line out, the length along the curve, which is significantly more than the depth. One Trolling Angles test showed that an 8 pound ball, with a large flasher, at 2mph, with 90 feet of line, the cannonball reached only 60 feet of depth.
An electronic depth finder may show the ball near the outer part of the transducer cone. It shows the straight line distance from the transducer to the cannonball, which is also significantly more than the depth. This is similar to using the line counter except it measures a straight hypotenuse rather than along the line’s curve.
A probe attached to or near the cannonball which measures water pressure may be more accurate, but is expensive. It also causes its own drag, so its only accurate for lines with probes.
Most charts provided on the web, even by downrigger manufacturers, are specific to certain rigs, and are imprecise or just plain wrong. They are also harder to read and use on the water than the Trolling Angles app.
Seriously, an app like Trolling Angles is the best way to determine cannonball depth.
