Returns a **Double** specifying the arctangent of a number.

**Syntax**

**Atn**
**(**
**
number
**

**)**

The required ** number**argument is a Double or any valid numeric expression.

**Remarks**

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.

The range of the result is pi/2 to pi/2 radians.

To convert degrees to radians, multiply degrees by pi/180. To convert radians to degrees, multiply radians by 180/pi.

**Note:** **Atn** is the inverse trigonometric function of **Tan**, which takes an angle as its argument and returns the ratio of two sides of a right triangle. Do not confuse **Atn** with the cotangent, which is the simple inverse of a tangent (1/tangent).

## Example

**Note:** Examples that follow demonstrate the use of this function in a Visual Basic for Applications (VBA) module. For more information about working with VBA, select **Developer Reference** in the drop-down list next to **Search** and enter one or more terms in the search box.

This example uses the **Atn** function to calculate the value of pi.

Dim pi pi = 4 * Atn(1) ' Calculate the value of pi.