in the "ThreePhase" source, there is a "Controls" tab. you'll see there:
control.addSlider("zscale", -256, 256, zscale, 10, y += 10, 256, 9).setWindow(controlWindow);
control.addSlider("zskew", -64, 64, zskew, 10, y += 10, 256, 9).setWindow(controlWindow);
the first two numbers are the range, and then it gives the default value (defined at the top of the file). if you know a more precise range for your scans, you could just try changing this.
alternatively, you could replace addSlider with addNumberBox like in this example:
http://www.sojamo.de/libraries/controlP5/examples/ControlP5numberbox/ControlP5numberbox.pdekyle