I use the MS scale that coin collectors use; it goes from 0-70 and is logarithmic, but MS 60+ is the only relevant part since any girl under an MS 60 is too ugly to consider putting a grade on (unlike coins). An MS 64 is a pretty girl (maybe a "7"), a 65 is somewhat beautiful (an "8?")and over that reflects mostly personal taste in how outstanding a girl can be. I've never seen an MS 70 and only a handful of 69's. 68's are rare but they exist. Most 'beautiful' girls top out at a 66 with a few 67's popping up now and then. My ATF is a 66 IMHO.
It's transferable from place to place but not medium to medium. In photos, girls get 1-2 grades deducted because they are retouched or otherwise inaccurate from what a girl really looks like. In movies they get maybe a 1 point deduction because when you see how they move, or how they talk, it can add back to their overall hotness despite movie makeup.
For me, an MS 65 in Chicago is the same as a 65 in Vegas. While some locals may have more hot women than others, it won't change my grade for any particular woman.