The ultimate pressure specification of a vacuum pump is the lowest pressure it can achieve at its inlet port. This pressure will be higher in the chamber (called end pressure) which the pump is connected to due to extra gas provided by leaks, outgassing, and input gas flows (where applied). The ultimate pressure is about one decade higher when Gas Ballast is on due to the extra gas flow the pump has to handle. "Partial ultimate pressure" is the ultimate pressure of the pump when tested with dry nitrogen as a reference gas. "Total ultimate pressure" is the ultimate pressure when normal ambient air is used for the test. The ultimate pressure of a pump depends on the internal construction of the pump and its general capabilities. As a large variety of pumps are available for different pressure ranges and applications, so the ultimate pressures can vary also. The application and the requirements of pumpdown including end pressure determines the pump choice.