Cardinal Points

Cardinal points are the markings around the outside of a round analogue gauge dial which define the measurement increment divisions.

The cardinal point or division markings on the dial face of a Bourdon tube pressure gauge can be separated by a large amount making it difficult to read the pressure precisely and therefore it is not possible to read the error directly when applying an exact calibration pressure setpoint.  

When calibrating Bourdon tube type or any other type of analogue dial pressure gauge you should adjust the pressure calibrator so that the applied pressure is set to the cardinal point on the pressure gauge.  The error can then be read to a much higher precision from the calibrator.