The Therma Differential digital thermometer is an ideal HVAC thermometer as it allows the user to use two type K thermocouple probes simultaneously. The display can be switched to show probe T1 or T2 temperature or the difference between probes T1 and T2 (T1-T2). This allows, for example, the temperature drop across radiators or the temperature rise or fall of two items to be measured.

The Therma Differential measures temperature over the range of -99.9 to 299.9 °C with a 0.1 °C resolution or 300 to 1372 °C with a 1 °C resolution. The thermometer features a custom, LCD display with °C, T1, T2, diff, hold, open circuit, low battery indication and an optional backlight. The unit incorporates an auto-power off facility that automatically turns the instrument off after approximately ten minutes, maximising battery life.

Each thermometer is housed in a durable, ABS case that has an integrated rubber seal to ensure complete water tightness and help reduce the possibility of damage in harsh environments.