Heavy Duty Series comprises four separate devices: Model HD200, a differential thermometer datalogger; Model HD300, a thermo-anemometer; Model HD500, a psychrometer with infrared thermometer; and Model HD700/HD750, a differential pressure manometer. The HD200 allows users to take differential temperature readings with dual Type K thermocouple probes as well as noncontact surface temperature measurements using an infrared thermometer probe. The HD300 provides simultaneous display of airflow in cfm/cmm or air velocity as well as ambient temperature. The HD500 combines the functions of a humidity meter, Type K thermometer and infrared thermometer. Finally, the HD700 can serve as a low range/high resolution gauge or measure differential pressure.