This water level is built from two tall stakes with markings and a long line of plastic tubing, filled with colored water. I used it to level the foundation. Here, I am checking the level of one of the boards used to form the foundation, inside the trench dug by the tractor. It doesn't matter how much the tube travels up and down, at the two ends, the water will always seek to be level, as long as there are no air bubbles inside.