In electrical terms this is analogous to measuring the voltage across a resistor to determine current where the pressure is voltage and the needle valve is resistance. So this is actually measuring flow rate as it varies with the immersion depth.

great PDF write up. say someone was to mount the tube on the wall where the water changes. What might a scale look like for it that could be posted with it?

By the tube, I assume you mean the manometer. The most accurate way to accomplish this would be to make a scale that is calibrated to your setup and then use that to measure the indicated water depth. This could consist of a paper scale glued to a ruler or a similar configuration. The reason you would want to use a separate scale is that the manometer reading is the distance between surfaces. If evaporation of water in the column occurs then a fixed scale would not be able to accurately measure this distance.
Of course, the more expensive and easier route would be to use a cheap single board computer with a differential pressure sensor to provide the data.