An analysis phase occurs automatically as each measurement is added or removed and before showing a graph. The calibration data is used by the analysis module to compute a curve data set, which is an approximation to the actual fishing line’s profile curve.
Invalid Data
If any of the line length and angle pairs of the calibration data are invalid or inconsistent, such that the analysis does not complete correctly, the analysis module will display an error message. You cannot graph or troll with this data. You may inactivate any length-angle measurement, or edit the calibration data by deleting invalid measurements or adding new measurements, and the analysis phase may be re-executed.
Flawed Data
In the Calibration page, the calibration is checked for reasonable consistency flaws, which are shown as red notations in the list of measurements. These flaws do not necessarily prevent analysis and use, but probably indicate that one or more measurements are not completely accurate. They are noted to help you correct obvious errors.
Angles Decrease
In a consistent set of measurements, as line length increases, the line angle becomes shallower. That is, angles decrease. For example, the angle at length 50 is always less than the angle at length 40. (The first derivative of the line curve decreases monotonically) If comparison of two adjacent measurements shows that the angle increases, a flaw is noted.
Curvature Decreases
As line length increases, the line becomes straighter, or curvature decreases. That is, angles will decrease at a lesser rate. For example, (if length intervals are equal), the difference of the angles at length 50 and 60 will be less than the difference of the angles at length 40 and 50. (The magnitude of the second derivative of the line curve decreases monotonically). If comparisons of 3 adjacent measurements show that curvature increases, a flaw is noted. This flaw will usually not change the final depth analysis much.
Submerged Line Increases
If the rod tip is held above the surface, as more and more line is released, angles approach but never reach zero. As the line becomes very horizontal, more line length results in very little but at least some more submerged line or depth. If comparison of two adjacent measurements shows that submerged line decreases, a flaw is noted. This condition usually occurs when the angle is too small and/or the length interval is too large compared to the previous measurement.
Note that submerged length is determined by subtracting unsubmerged length from total length, and unsubmerged length is determined with simple trigonometry on the angle and the rod tip height. The curve of the submerged line is not involved.
Don’t Sweat it
Arguably, the Trolling Angles method is at least as accurate as other methods in common use to determine trolling depth.
It’s not really possible to measure fishing line angles absolutely precisely or accurately in real life. The angles become especially harder to measure accurately and to differentiate as they become shallower, especially under 5 or 10 degrees. You may find yourself re-measuring and making some judgement calls about which measurements to keep. It’s not necessary or practical to be absolutely perfect, but it is easy to get close enough for good results. And most fish will probably not notice the difference.
