### ATN(number)

Returns the arc-tangent of a number in radians (Double).

 number The number you want the arc-tangent of (Double).

 REMARKS
 * This function takes the ratio of two sides of a right angled triangle 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.* The arc-tangent of a number is the inverse of the TAN function.* The "number" can be any valid numeric expression.* The value returned can be in the range -PI/2 to PI/2.* If your argument is in degrees, multiply it by PI/180 to convert it to radians.* If your argument is in radians, multiply it by 180/PI to convert it to degrees.* The reciprocal of this function (1/TAN) is called the cotangent.* The equivalent Excel function is Application.WorksheetFunction.ATAN* The equivalent .NET function is System.Math.Atn* For the Microsoft documentation refer to docs.microsoft.com

`Atn(1) = 0.785 Dim lPi As Long lPi = 4 * Atn(1) `