Recently we have acquired high accuracy resonant silicon gauges of two different ranges, one 130 kPa full scale and the other 1 kPa full scale, for measurement of the initial and final pressures. These gauges have been utilized in a cumulative expansion process for the measurement of the volume ratio of the NPLI Static Expansion System which is nominally 2820. With these new gauges, and with the use of calibrated Platinum Resistance Thermometers mounted inside the vacuum chambers, it has been possible to measure the volume ratio with a relative expanded uncertainty (k=2) of 0.0015. The standard thus characterized has been used to calibrate SRGs at a number of pressures in the range 0.1 Pa to 1 Pa in steps of 0.1 Pa. The Gauge Constant at each of these pressures, defined as equal to the ratio of the indicated pressure to the true pressure is then plotted against the true pressure. The resulting straight line plot has a negative slope and its intercept equals the gauge coefficient. The two SRGs, NPL-0 and NPL-2 thus calibrated are used (i) as a device for measuring the pressure rise in the flowmeter of the NPLI orifice flow system and (ii) as a secondary standard for the calibration of the user gauges.