sliding bar

i have 2 images used for making a slider. one is fixed called imgvolbar and other moves called imgvolbtn on it and used it for volume bar.now the problem is the movement is not very free and i need to move it very freely from left to right.code goes here.

Dim btn As boolean
Private Sub imgvolbtn_MouseMove(Button As integer, Shift As Integer, X As Single, Y As Single)
Dim x_pos As Integer
Me.ScaleMode = 1
x_pos = Me.imgvolbtn.Left + X

If (btn = True And (imgvolbar.Width - 200) + imgvolbar.Left > x_pos And imgvolbar.Left < x_pos) Then
Me.imgvolbtn.Left = x_pos
ElseIf (imgvolbar.Left > x_pos) Then
Me.imgvolbtn.Left = Me.imgvolbar.Left
End If
Me.ScaleMode = 3

what should i include for the imgvolbtn to move freely on imgvolbar?

thanx in advance.
regards.