[mamelukesabre]

Wow, I am not understanding this AT ALL. looking through a polarized lens at a cloudy sky will tell you NOTHING. I’m assuming looking through a polarizing crystal gives the same effect.

[Kirkwood]

No, this makes sense. And it is very clever.

[Oztrich Boy]

No it works http://www.great-landscape-photography.com/polarizing-filter.html

If rotating the polarizing filter darkens the sky (or clouds) you are ponting it at right angles to the sun position.