Simple trig gone drastically wrong

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?

VB Code:

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.

Not *exactly* sure what you're trying to do, but i'll help out anyway.
My suggestion is mainly to do with shotening your program.

1) Use loops:

VB Code:

For loopval = 0 to 15
if currenttemp = selectedtemp + loopval then a = 12*loopval
next loopval
 
If currenttemp> (selectedtemp + 15) then a = 180
If currenttemp< selectedtemp then a = 0

As for your gauge, what you need to do is something like this:

VB Code:

Line(fix_point_x, fix_point_y)-(fix_point_x + sin(Degree_Val*180/Pi), fix_point_y+ cos(Degree_Val*180/Pi))

where:
Pi = 3.14159
fix_point_x = the x value of where the meter's needle is fixed.
fix_point_y = the y value of where the meter's needle is fixed.
Degree_Val = the angle of the needle. (0 = right, 90 = up, 180 = left, 270 = down)

N.B. the cos() and sin() might be around the wrong way.
AND: the 180/Pi *might* be Pi/180, i'm not sure exactly how to convert radians to degrees.

ahh yes thank you

but the conversion was one thing i did know :)
180/Pi is radians to degrees
Pi/180 is degrees to radians

OK, hope it works.
I had better try to remember which way round, as i'm sure i'll have to use it soon.

Anyway, GO AUS!! over 40 Gold medals in Man, UK :D :p