hi, here is my problem. Function t1(sita As Double, t0 As Double, l0 As Double) As Double sita = (sita - 90) / 180 * 3.14159265 t1 = t0 - l0 * Tan(sita) End Function 'ok Function t2(sita As Double, t0 As Double, l0 As Double, l As Double) As Double t = t1(sita, t0, l0) MsgBox sita t2 = t + l * Tan(sita) End Function Sub test() MsgBox t1(95, 7.5, 20) MsgBox t2(95, 7.5, 20, 120) End Sub in MsgBox sita the sita is not 95, why. thank you.