Measurement range
Which measurement method offers an appropriate measurement range? Is one single method sufficient or is it necessary to combine different methods? Are combination gauges applicable?

Accuracy, reproducibility, response time
What measurement accuracy does the vacuum application require? Which measuring method offers sufficient accuracy? What reproducibility and response time of the sensor is necessary?

Composition of the process media
Are correction factors for gas-type dependent measurements necessary and known? Is the gas composition variable?

Process conditions and environmental conditions
To which process media or conditions is the sensor exposed? (media: corrosive, hazardous, oxidizing / deoxidizing, etc.; process conditions: contaminating or coating, low / high temperatures, high voltages, magnetic fields, glow discharges and other plasmas, fast pressure rise or pressure shock, etc.).
Is a protection of the gauge in front of the inlet port necessary, by means of a baffle, a valve, a bent tube etc.?
Which requirements result from environmental conditions? (vibration resistance, protection against contaminants and water, mechanical robustness, climatical and geographical conditions, ionizing radiation, etc.) Is there a danger of ignitable gas mixtures? Are explosion-proof gauges required?

Bake-out capability
What temperature stability is required for the gauge and the gauge cable? Need temperature sensitive parts to be removable?

Readings display
Is a pressure display required? If yes, is an active gauge with integrated display appropriate or a separate display unit for one or more gauges?

Process control, data logging
Which setpoints, analog outputs, PC or fieldbus interfaces need to be available?

Signal transmission
Which type of signal needs to be transmitted over which cable lengths and in which quality?