well, okay, this is exactly what I want to do...
lets take a tredmill for example.
I want to make, say a training program, where I tell the runner how fast he has to run. let say this speed is going to vary. So, I have a speed versus time line. with the left edge being zero and the right being 100 feet per second, the line will start at the top and scroll down. This is theoretical speed. Now, we take the cursor which is actual speed of the tredmill (I can handle all the hardware to get the speed from the transducer into a variable). This will scroll left to right (left zero right 100). The name of the game is for the runner to keep his cursor over the line as it varies. If he is off the line, say by 2 fps, the cursor turns red. I can deal with all the hardware and all the other logic behind it, its just this graphical subroutine that has me stumped.