I would like to measure the DoLP of outside daylight at the horizon with the sun overhead (midday in summer). Found this equation: DoLP = (reflectanceS - reflectanceP) / (reflectanceS + reflectanceP) Where S and P are defined: “The two orthogonal polarization planes are s, perpendicular to the plane of incidence defined by the surface normal and the incident ray, and p, parallel to the plane of incidence.” (A diagram showing what this statement refers to would be helpful as I am not familar with the terms used.) I know that to get the S and P amplitude values I need to measure the light through a linear polarizer turned to one angle and then a different angle. Can someone tell me what two angles I need to rotate the polarizer? Thanks!