Protected variable?

I wasn’t sure exactly how to phrase this question but it is a problem that has been bugging me for a while now and I’m sure has quite a simple answer!

I have a scroller that moves faster the longer a button is pressed i do this by starting an incrementor (i+=whatever) on the press and clearing it on the relase. _x of the scroller is made to equal the incrementor. what I want to do is read what the incrementor is equal to when the slider reaches a certain target and store that number in variable that doesn’t change until I want it to. - e.g. when the slider reaches the x position of 600 I want to read what number the incrementor is at and not change i.e. something like this

if (_root.slider._x > 599 && _root.slider <601){
var whatisincrementor = i;

Now obviously the problem with this is that var whatisincrementor continues to increase as does the incrementor (i) - what I want is to store the value of the incrementor at 600 ONLY and not to continue increasing!! any help much appreciated - I really mean that!