The capacitance diaphragm gauges (CDGs) have been in use for a few decades and have been employed as transfer standards and reference standards. Despite their drawbacks, they continue to be used due to their ruggedness and UHV compatibility. A CDG consists of a sensor and an electronics control unit to display the pressure. To overcome the problem of ambient temperature variations, a heater is provided in the sensor to maintain it at nominally 45 °C. In a differential CDG, zeroing is done with both sides kept under vacuum. Afterwards, the system check (SC) is performed. This parameter is compared with the value given in the calibration sheet. A deviation between the two values is an indicator of the gauge needing re-calibration. A study has been performed to establish the link between the calibration factor (CF) and the SC, between the SC and the temperature of the CDG sensor and between the temperature and the shift in the sensor zero. A Resonant Silicone Gauge of 130 kPa f.s. range was used as a secondary standard for the calibration of the CDGs. The plots of CF against the pressure at different temperatures show that over a range of pressures, typically 100-1000 torr, the CF varies linearly with pressure and both the slope and the intercept values of this linear fit go on increasing as the temperature increases from about 290 - 318 K. Each temperature value corresponds to a different value of the SC. At 318 K, the CF tends to become a constant over the pressure range 100-1000 torr, meaning thereby that the slope becomes zero. Hence it can be said that the slope and intercept of the CF vs. pressure curve are a function the SC. Plots of the different values of the slope and the intercepts against the SC values give linear fits from which we can calculate the slope and the intercept values for any particular SC value. Hence we can calculate the CF at any pressure in the range 100-1000 torr, for any temperature between 290-318 K.