grade (slope)

A grade (or gradient) is the pitch of a slope, and is often expressed as a percent tangent, or "rise over run". It is used to express the steepness of slope on a hill, stream, roof, railroad, or road, where zero indicates level (with respect to gravity) and increasing numbers correlate to more vertical inclinations. There are three common numbering systems: the angle from horizontal in degrees,as a percentage: the tangent of the angle of inclination: the ratio of the altitude change to the horizontal distance (this is the more common percentage type), oran alternative definition as a percentage: the sine of the angle: the ratio of the altitude change to the surface length between any two points on the grade—also known as rise to run (not to be confused with the "rise over run" taught in grade-school geometry).
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