I **think** grade is actually calculated by the edit software based upon GPS fixes and GPS elevations / altitude are notoriously inaccurate. At high speeds (like a car and aircraft) the inaccuracies tend to average out.
Pitch and roll , again I **think**, are actually recorded based upon sensors within the camera.
I found that I had poor GPS coverage in spots at Windrock which caused all sorts of interesting gauges like speed bouncing all over the place and tracks that were straight lines ....
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