Malcolm Simmons, Peter Cope, Angle and Rotation: Effects of Different Types of Feedback on the Quality of Response, Educational Studies in Mathematics, Vol. 24, No. 2 (1993), pp. 163-176 ...

Hopefully that's clear. Once I have the angle of rotation (or rather, both angles, since there are of course two answers 180° apart), I can handle the rest.

This rotated light is partially blocked by a second filter parallel to the first but allowed to pass completely through a second filter, which has been rotated by an angle equal to the rotation of the ...