Spinning rotor gauges (SRGs) act as transfer standards for measurement of pressures in the range 1 Pa to 10@super-4@ Pa. There are two methods for the measurement of the gauge calibration factor. In the first, the gauge is connected on a primary standard and pressures in the range 0.1 to 1 Pa are generated and the viscosity parameter is entered as equal to zero in the gauge controller. Then a plot of the ratio of indicated pressure to the real pressure ( =@sigma@@subeff@) against the real pressure is obtained as a line with negative slope. The intercept of this plot for the real pressure equal to zero gives the gauge coefficient. In the second method, the same procedure is adopted but the actual value of the viscosity of the test gas is entered into the controller. The plot obtained in this case is a horizontal line. The average of the different @sigma@@subeff@ values gives the gauge coefficient. This paper gives the results obtained at the National Physical Laboratory (N. Delhi)for the calibration of three SRGs by the two methods and shows that agreement of ±0.1 % is obtained in all the three cases.The real pressures were generated using the NPL primary standard based on the principle of static expansion.