The checkbox "complementary" graphically shows the co- versions of the trigonometric functions. Angles are shown as central angles in a circle of radius 1 measured in degrees. The angle is the complementary angle of , so, for example, the cosine of is the same as the sine of the complementary angle . Arc length and coarc length are not "official" trig functions, but for completeness and because they are simple, the author put them in. They are equal to the radian measures of the angles and , respectively.