Calculates the arctangent of a number.
ATan ( expression )
| expression | Any valid numeric expression. | 
The result of 4 * ATan(1) is pi.
#include <MsgBoxConstants.au3>
Example()
Func Example()
    ; Assign a Local variable the arcTangent of 0.5.
    Local $fArcTan1 = ATan(0.5)
    ; Display the result.
    MsgBox($MB_SYSTEMMODAL, "", $fArcTan1 & " rad.")
    ; Assign a Local constant variable the approximate PI number.
    Local Const $PI = 3.141592653589793
    ; Assign a Local variable the formula to switch from radian to degree (equals to one radian in degree).
    Local $fRadToDeg = 180 / $PI
    ; Assign a Local variable a number in degree.
    Local $fArcTan2 = $fRadToDeg * ATan(1)
    ; Display the result.
    MsgBox($MB_SYSTEMMODAL, "", $fArcTan2 & " deg.")
EndFunc   ;==>Example