Force balancing: Pressure-well balanced fused quartz Bourdon tubes use a spiral Bourdon tube to exert pressure over a pivoting armature containing a mirror, the reflection of the beam of light through the mirror senses the angular displacement and current is placed on electromagnets around the armat

Calibration is vital in order that the pressure gauge offers exact readings more than the range of pressures it can be made to measure. So, for instance, pressure head could possibly be prepared "742.2 mmHg" or "4.2 inH2O at 59 °File" for measurements taken