The sealed finish is totally free to move a pointer more than a scale in accordance with the used pressure inside the tube, coming into in the open up stop. Other mechanical products like diaphragms and bellows also can measure gauge pressure. Among hydrostatic ones, the u-tube manometer is effective. http://pressuregauge76420.theobloggers.com/15098003/helping-the-others-realize-the-advantages-of-pressure-gauge