The Series 9555 are portable, hand held, Multi-Function Ventilation Test Instruments. These instruments are available with or without a differential pressure sensor and are designed to work with a wide range of plug-in probes. The probes allow users to make various measurements by simply plugging in a different probe that has the features and functions best suited for a particular application. They are designed to measure air velocity, temperature, humidity, CO and CO₂. Calculations include air flow, heat flow, turbulence, wet bulb and dew point temperature.

The probes can be ordered at any time and include a data sheet with certificate of traceability. When its time for servicing, only the probe needs to be returned since all the calibration data is stored within the probe.