This is the scale (often enumerated 1 - 10) that measures the attractiveness of members of the opposite sex. A female, for example, that has a squint-factor of 0 is attractive without the need to squint while looking at her. Conversly, a woman with a squint-factor of 10 is only attractive while squinting considerably and maintaining a very optimistic interpretation.
See Also: Beer Goggles
I usually like to make the magic happen with the lights on, but since she was like a squint-factor of 10 I had to turn that shit off.