I believe that there are two HB scales. Both are relevant for different things- but I believe that one is a little more useful than the other for sharing experiences.

TL;DR: It's not how hot she looks. It's how hot she feels she is.

#1: How you value her

This is for telling you bros "yo man I totally hit that 8 last night". It's entirely subjective and everyone has their preferences. With girls rating guys it's even more subjective.

10: Marry her ASAP

9: "Perfect"

8s+ are models

8: She's hot.

7: She's hot but not the hottest.

6: Cute, above average

5: Typical

4 ≥: Came out of Davy Jones' locker

Pros: You can brag to your buddies

Cons: Read ahead.

#2: How she values herself

This dictates how you proceed with your 'game' and interactions. Not how hot she looks, it's how hot she feels she is.

Does she know she's hot and values herself highly? Is she cocky? Then you tease her more, bother her, show generally less interest, make sure her friends like you.

Is she the kind of girl One Direction sang about who doesn't know she's beautiful? Here you can get away with showing more interest. Don't tease her as much. You can be a bit more direct with your intentions

The scale is how the girls subconsciously rate themselves on the HB1-10 scale.

10: Thinks she's absolutely perfect.

9: Thinks that she's hotter than every other girl

8: Thinks that she's attractive and most likely the hottest of her friends, but knows that she's not the hottest

7: Thinks she's likeable by guys, knows there are more attractive girls out there

6: Thinks that she's a bit above average

5: Thinks she's just a typical girl

4 ≥: Thinks she's unnatractive

Pros: More accurate indicator on how to game her

Cons: Looks can be deceiving

Let's put down some hypotheticals. I think she's an 8, she thinks she's a 10. I would 'game' her differently than this girl, who I think is a 9 but she thinks she's a 7. I tease the first girl more than the second girl and show more interest to the second.

It's not how hot she looks. It's hot hot she feels she is.