# NMI – Calibration of Pressure Measurement #SWI2006

In pressure measurement, the value of pressure is determined by dividing the force exerted on a piston by the effective area of the piston. The effective area of the piston may differ from the actual area because of irregularities at the piston edge and because of leakage through the thin cavity between the piston and the enclosing cylinder. The associated uncertainties constitute the largest contribution to the overall pressure measurement uncertainty. The various metrological institutes each use a different method of calculation of the effective piston area for a given piston-cylinder combination. The figure below shows the results of a comparison study in which six sets of measurement data were given to each of the six participating institutes (taken from doi:10.1088/0026-1394/42/6/S11).

The details of these methods of calculation can also be found in the same reference. The question for the Study Group Mathematics with Industry 2006 is Can we compare the different methods of calculation? Which is best? Can they be improved any further?