OptomCAS Science GPA?

I know that when you apply, OptomCAS will generate different GPAs. I've even visited the site, but I'm still a little confused.

So there's an overall GPA and a science GPA. I wanted to know what constitutes the science GPA that's generated from OptomCAS?

Is it all of the science courses taken during undergrad or is all of the prereq's (including math, psychology, humaitites, etc)?

Thanks in advance!