It's really simple. When you meter through the lens with a polarizing filter, the readings will change as you rotate the filter. However this is just the meter being fooled by the polarizer. Don't go by that. Filter factors for a polarizing filter are usually 1.3 to 1.7 stops. I use 1.5 stops and I'm happy with that. Take your meter reading without the polarizer (or use a hand held meter) and add 1.5 stops more exposure. That's all you need to know, and it works every time. The amount of polarization you dial in doesn't matter. The filter factor is constant. To the OP, since you already have a circular polarizer, you can use it with anything and it works exactly the same as a linear polarizer.