I think I discovered a tiny problem in your 'relative proportions' formula picture. you have

    y'   y
    -  = -
    z'   z'

in the first line. The z' on the bottom right should be just a z, right? Other than that, this is perfectly clear, and I understood it even though I just came out of high school and haven't started college yet! Absolutely fantastic work!

EDIT: Fraction format