The .Plan

The equation that describes the quality of the female rear end, according to [David Holmes, a psychologist at Manchester Metropolitan University], is

(S + C) x (B + F)/T - V,

where S = Overall Shape (“including tendency to droop”), C = Circularity, B = Bounce Factor (not to be confused with “wobble”), F = Firmness (with perfect being “like a comfy bed”), T = Skin Texture and V = Vertical Ratio (the goal: “on the top-heavy side of symmetrical”). For the male rear end, the equation replaces bounce, circularity and vertical ratio with M (Muscularity), L (Leanness) and O (Overall Symmetry).

The numbers you plug in to the equation come from a list of descriptions. To calculate B for Bounce: “After one flick it wobbles for 30 secs” gives you a 2, whereas “during aerobics it doesn’t even quiver” gives you a 5. And so on.
–Rebecca Skloot, “Tushology”, New York Times Magazine, Dec 10, 2006