Rational slice discrete
Compare adjacent options (e.g. pizza sizes) by marginal price per unit of “value” (diameter or area), spot diminishing returns, and see simple heuristics for whether the menu order looks self-consistent.
Your options
Size is the linear measure you care about (for pizza, diameter in inches). “Value” is either that number or the circular area from it, depending on the mode below.
Educational tool: “Rational” is a hand-tuned plausibility check, not a statement that a price is wrong or that you should order anything in particular.