Function InvAngle(inv As Double) As Double Dim angle_rad As Double angle_rad = (3 * inv) ^ (1 / 3) ' starting approx For i = 1 To 5 angle_rad = angle_rad - (Tan(angle_rad) - angle_rad - inv) / (1 / Cos(angle_rad) ^ 2 - 1) Next i InvAngle = angle_rad * 180 / 3.1415926535 End Function