ActionScript 2.0 :: Delay In Slider Bar Functionality So Value Change Slowly

I have created a slider bar using AS2, when I say slider bar I mean similar to what you would find on a mixing desk in a music studio, i.e. you 'slide' the button up and down, changing the value associated with it. My slider bar changes a value that is written on the screen, i.e. it goes from 0 to 100 as you slide the button up. Now I want to change this so that when you slide the button the value starts to slowly change, and eventually reaches the value you've pushed the button to but after you've finished moving the button. Not sure that makes sense! To put it another way: if it takes you half a second to move the slide button from the bottom to the top, it will take 10 seconds for the value associated with it to reach 100.

Below are the relevant bits of code:
This starts the slider action when the button is pressed:
Code:
function onPress() {
this.startDrag(false, sliderMin, 515, sliderMax, 515);
}

This determines the displayed value from the slider bar position. Obviously right now the value changes instantly when you move the slider button
Code:
function onMouseMove() {
_root.powerGraph.totalPower = Math.round((_root.startMenu.coal1Slider._x - sliderMin) / (sliderMax - sliderMin) * 100);
}

This is used to display the value:
Code:
function onEnterFrame() {
this.createTextField("outputPower", _root.startMenu.getNextHighestDepth(), 130, -20, 190, 101); .....

This stops the button movement:
Code:
function onRelease() {
this.stopDrag();
}