How can I determine what degree of polarization my polarized film is? I have a piece of either circular or linear polarized film that I had laying around, however, I have no knowledge of the degree of polarization that the film has. How can I test to see what the degree of polarization is. I have my monitor and other screens to test it against but again I do not know the polarization degree of the monitor either. Can someone help?
 A: Surely you need second polarizer with known properties. 
In the lab we can surely use something fancy like Glan–Taylor prism, but it is not required. The easiest way is to use a piece of flat glass rotated to Brewster angle as a polarizer. For regular glass Brewster angle is ~56.62°.

Please keep in mind, that many linear polarizers for photography convert linear light to circular polarization after the filter (so that it does not interfere with DSLR cameras focusing system - much less important with mirrorless). 
A: I may be wrong but find a flat level shiny surface like a glass table top and stand where you can see a good strong reflection. Down low where the angle of reflection is wide is better. The photons coming at you should be polarized mostly horizontally. Look through the polarizer at the reflection and slowly rotate it. It should get darker when the polarizer is vertical and brighter when the polarizer is horizontal.
A: You could use haidingers brushes to see the polarization of your LCD with your eyes and then use that to find the polarisation of your filter.
