Simple trig gone drastically wrong

[Jack Daniels]

hi this program should draw a needle like line for a guage

but i have got the lengths wrong for the needle when it is on different angles, can anyone make sense of where i have gone wrong?

Private Sub Timer1_Timer()
Dim currenttemp, selectedtemp, a, b, c As Integer
selectedtemp = selectedtemptext.Text
currenttemp = Int(((selectedtemp + 15) - selectedtemp + 1) * Rnd + selectedtemp)
'read currenttemp
Select Case currenttemp
Case Is = selectedtemp: a = 0
Case Is = (selectedtemp + 1): a = 12
Case Is = (selectedtemp + 2): a = 24
Case Is = (selectedtemp + 3): a = 36
Case Is = (selectedtemp + 4): a = 48
Case Is = (selectedtemp + 5): a = 60
Case Is = (selectedtemp + 6): a = 72
Case Is = (selectedtemp + 7): a = 84
Case Is = (selectedtemp + 8): a = 96
Case Is = (selectedtemp + 9): a = 108
Case Is = (selectedtemp + 10): a = 120
Case Is = (selectedtemp + 11): a = 132
Case Is = (selectedtemp + 12): a = 144
Case Is = (selectedtemp + 13): a = 156
Case Is = (selectedtemp + 14): a = 168
Case Is = (selectedtemp + 15): a = 180
Case Is > (selectedtemp + 15): a = 180
Case Is < selectedtemp: a = 0
Case Else
End Select
'12,24,36,48,60,72,84,96,108,120,132,144,156,168,180
'a = currenttemp - selectedtemp
 
Cls
If currenttemp < (selectedtemp + 1) Then
    'set g to 0 if current temp is colder then selected temp
    'and draw meter to 0
    g = 0
    Line1.X1 = 500
    Line1.Y1 = 500
    Line1.X2 = 140
    Line1.Y2 = 500
    Else
    If a > 179 Then
        'set g = 1 and draw meter at 180 because temp is too hot
        g = 1
        Line1.X1 = 500
        Line1.Y1 = 500
        Line1.X2 = 860
        Line1.Y2 = 500
        Else
        If a > -1 And a < 91 Then
            'draw meter if temp falls on left hand side
            b = -(360 * (Sin((a) * 0.017453292)))
            c = -(360 * (Cos((a) * 0.017453292)))
            'Line (1000, 1000)-Step(c, b)
            Line1.X1 = 500
            Line1.Y1 = 500
            Line1.X2 = c
            Line1.Y2 = b
            Else
            If a > 90 And a < 181 Then
                'draw meter if temp falls on right hand side
                b = (360 * (Sin((a - 90) * 0.017453292)))
                c = -(360 * (Cos((a - 90) * 0.017453292)))
                'Line (1000, 1000)-Step(b, c)
                Line1.X1 = 500
                Line1.Y1 = 500
                Line1.X2 = (b + 500)
                Line1.Y2 = c
            End If
        End If
    End If
End If
End Sub

thanks for taking the time to even look at this.