Level position measuring method, level marking method and level marking apparatus comprising a tube, capable of directly measuring a height

A level marking apparatus capable of directly measuring height comprises an elastic synthetic resin tube. One end of the tube is secured to a pressure sensor capable of producing an output voltage and air-tightly sealed, and the other end of the tube is connected to a reference instrument, which has a larger diameter and is shorter in length than the tube. The tube is totally filled with low viscosity macromolecule liquid. Moreover, the pressure sensor is connected to a micro computer programmed to find an average value of fluctuation waveform within a certain cycle of output voltage of the pressure sensor. The micro computer also calculates and memorizes a reference level based on a pressure difference between the reference instrument and the pressure sensor when placed at different heights. Additionally, a marking device is connected to the pressure sensor, and it is actuated by an ON signal from the pressure sensor. The ON signal is dispatched when the marking device is at the same height as the reference level. The marking device and the pressure sensor are secured to a lift, capable of moving up and down along a staff plate. The marking device automatically indicates a level mark when a level is reached equal to the reference level.