Infinite upward scroll with defined bottom in AS3 - actionscript-3

Question

I am trying to make a display that takes an input number and displays that number centered vertically on a strip along with the numbers above and below it, appropriately spaced. That much works - my problem is with getting it to bottom out at zero. I don't want to have negative numbers or even tick marks below zero.
You can see the file in question here: http://www.fastswf.com/r58wGg0
In that file, the left is what the final version will look like (masked - giving the illusion that it is moving infinitely) and the right is unmasked, showing the actual movement of the movieclip and text boxes. The input number is based on mouse position so slowly move your mouse around to see the action.
And here is my code.
var labelSpacing = 500;
var tickSpacing = 18;
function updatePosition(currentValue){
tape.y = ((currentValue/100)%5)*tickSpacing;
current.y = (((currentValue/100)%5)*tickSpacing)+170.85;
plus1.y = (((currentValue/100)%5)*tickSpacing)+82.85;
minus1.y = (((currentValue/100)%5)*tickSpacing)+259.9;
current.text = (Math.floor(currentValue/labelSpacing)*labelSpacing).toString();
plus1.text = (Math.floor(currentValue/labelSpacing)*labelSpacing+labelSpacing).toString();
minus1.text = (Math.floor(currentValue/labelSpacing)*labelSpacing-labelSpacing).toString();
}
Is there a way to modify this so that it changes its behaviour near zero so that it displays correctly?

Answer 1

Hmm, normally such indicators do allow displaying values below zero. But, for your purpose, you can use a limited currentValue to use in your calculations, but preserve the old value in case you need to display something else based on actual currentValue too.
function updatePosition(currentValue:Number):void {
var cappedValue:Number=currentValue;
cappedValue=Math.max(cappedValue,1.0*labelSpacing);
// experiment with this constant ^^^ to achieve desired result in production
tape.y = ((cappedValue/100)%5)*tickSpacing;
// and use cappedValue in place of currentValue in calculations
// rest of code
}