Probabilities under normal curves or any shape probability distribution function are measured as areas under the curve. It helps to have an integral calculus in

Probabilities under normal curves or any shape probability distribution function are measured as areas under the curve. It helps to have an integral calculus intuition for comparing p(0.1<x<0.5) to p(0.5<x<0.6). It helps to have a multi variate vector distance interpretation of length for error and variance magnitude.