I’m not sure how all of these inputs work, but using the built-in tablet tester, it seems there are two sensors: TX and TY, which is the measure of tilt in horizontal (X) and vertical (Y) direction (where XY is the plane of the tablet, and the Z axis is perpendicular to X and Y).
Each sensor can go from -60 to 60 (depending on whether we’re going in the -X or +X direction, for example). I guess this is where the “60” figure comes from. However, there’s a twist! Neither perfectly perpendicular or horizontal pen orientation is registering! It will clamp to 0 or 60 before that. It’s something like this, looking from the side:
However, the “stability” of the sensor is the best near 60 degrees, while near 0 degrees the jitter is the largest.