This is a model to find the angle of a windshield wiper, the angle of the wiper is important to reduce noise when cleaning. This angle should be close to perpandicular as possible to ensure the least chatter and a smooth transition when switching wiping directions, this point is marked with a peak on the scale at 0 degrees.

This is meant to fit the hook type wiper connection, probably close to the ISO 9259:1991 hook standard, not measured but looks about right :)