How to control how the slider bar applied the commands

Hi

I am adding a slider bar to an application. Is there a way that I can tell when the value has changed and exh time it changes it undoes the last function and applies the new one. The code I am using looks like this
Dim text1 As String
Dim text2 As String
Dim title2 As String * 13
Dim sliderval As Integer


ret = IpDocGetStr(INF_NAME, DOCSEL_ACTIVE, title)
 text1 = title
 text2 = orig

If text1 = text2 Then
sliderval = Guihigh.Slider1.Value



ret = IpWsOverlay(overlay, sliderval, 0)

I need the slider val to be one function between two images at the moment it changes each time it is moved but then keeps applying the function rather than just changing it.
Any help appreciated.