Bourdon tube pressure gauge is used for measuring high as well as low pressure. It consists of metal tube of approximately elliptical cross-section. This tube is bent in the form of a segment of a circle and responds to pressure changes. The pressure acts equally on every square inch of area in the tube. When pressure is applied, the tube will straighten out until the difference in force is balanced by the elastic resistance of the material composing the tube. When one end of the tube is attached to the guage case, the internal pressure causes tube to expand. These are generally made up of brass or nickel steel. The guage is calibrated against known pressures to ensure accurate readings. The working parts are enclosed within a protective case of metal, plastic or similar material with the dial visible through a clear glass or plastic face. This converts the measured parameter directly into a visual display on dial scale, from which it can be recorded. This is used to measure the pressure. This is also used to measure the water depth and hence to reduce relative heights.