grade

   1. a unit of angle measurement equal to 1/400 circle, 0.01 right angle, 0.9°, or 54'. This unit was introduced in France, where it is called the grade, in the early years of the metric system. The grad is the English version, apparently introduced by engineers around 1900. The name gon is used for this unit in German, Swedish, and other northern European languages in which the word grad means degree. Although many calculators will display angle measurements in grads as well as degrees or radians, it is difficult to find actual applications of the grad today.

   2. a measure of the steepness of a slope, such as the slope of a road or a ramp. Usually stated as a percentage in the U.S, the grade is the same quantity known as the slope in mathematics: the amount of (vertical) change in elevation per unit distance horizontally ("rise over run"). Thus a 5% grade has an elevation gain of 0.05 meter for each meter of horizontal distance, or 0.05 foot for each foot of horizontal distance. Grades are also stated as ratios (1/20 grade or 1 in 20 grade) and in some countries as a permillage (50^o/oo grade). The angle of inclination, in grads or grades¹, is not equal to the percentage grade in this sense: for a 5% grade the angle of inclination is about 2.86° or 3.18 grads.

   3. a measure of quality for ball bearings. A bearing of grade g is required to be spherical to an accuracy of g parts per million (g 10^-6). Thus lower grade numbers represent better bearings; a 25 grade bearing is spherical to within 25 ppm, but a 1000 grade bearing is only spherical to within 1000 ppm, or 0.1%.