First of all I'm not even sure if [line/~] is the best object for what I'm trying to do.
Here is an analogy of what I would like to do: You have a balloon and you can fill it up with air at a constant rate. Press a button to fill it up to it's capacity without popping it. Release the button to deflate the balloon at the same constant rate. And you have the ability to press the button on or off midway through filling up the balloon to try and keep it within a range manually.
I have messed around with [line] and [counter] but not able to come up with anything that works or is practical. Any thoughts?
Thanks in advanced.