In Access, the Atn function returns a double containing the arctangent of a number.
The syntax for the Atn function is:
Atn( number )
The required number argument can be any valid numeric expression. The Atn function takes the ratio of two sides of a right triangle (number) and returns the corresponding angle in radians. The ratio is the length of the side opposite the angle divided by the length of the side adjacent to the angle.