Microsoft® Visual Basic® Scripting Edition Tan Function 
Language Reference Version 1

Returns the tangent of an angle.
Tan(number)The number argument can be any valid numeric expression that expresses an angle in radians.
Tan takes an angle and returns the ratio of two sides of a right triangle. The ratio is the length of the side opposite the angle divided by the length of the side adjacent to the angle.To convert degrees to radians, multiply degrees by pi/180. To convert radians to degrees, multiply radians by 180/pi.