Smith's Scale is basically a scale used by men to determine a girl's overall looks. Most people use the treditional 1-10 scale when judging girls, but the Smith's Scale is using two scales to determine a girls overall rating and if they're good girlfriend material.
The first scale in Smith's is the looks scale. This scale is on 1-10 and it determines how they look. This has to do with their ass, tits, face, and overall looks. This scale is generally used when you want to determine a girls overall looks.
The second scale in Smith's Scale is the inside scale. This scale is also on 1-10 and it determines what the girl is like on the inside (not sexually). For example, the inside scale determines; how smart the girl is, personality, pet peeves, future thoughts, etc. This scale is usually used when you want to determine if the girl is real girlfriend material.
In the end of judging you can add up both of the scales and divide by two to get the girl's overall. For example, if a girl had a 6/10 looks, but a 9/10 inside she would be a 7.5/10 overall.
Me: Damn, look at Alanna over there. Her looks are 8/10 but her inside is a 2/10. She is definitely not my type.
Friend: Why are you using two different scales?
Me: I'm using Smith's Scale to determine the girl's overall and if she's girlfriend material. Overall Alanna would be a 5/10.