Robinair (10945 Dial Thermometer, 0&deg; to +220&deg;F Robinair Pocket Dial Thermometer with a large, easy to read, black on white 1-3/4 inch face Perfect for checking automotive, home, or commercial A/C performance at the vent Reads 0 to +220 degrees F Convenient pocket-clip carrying case protects the thermometer when not in use but keeps it handy for easy access when you need it Adjustable design ensures accuracy - simply twist thermometer face to known temperature (32F ice water works well) while holding 10 mm nut on base with a wrench