Sturdy plastic for better readings, able to withstand everyday use and abuse. Ideal for swimming pool water thermometers, pool spa thermometers, hot tubs, ponds and all other types of swimming pools. Convenient for storage and easy to use. Simple tools for measuring the temperature of swimming pools, hot tubs, etc. Swimming pool maintenance is essential. Double Fahrenheit and Celsius temperature display. Maximum temperature: 120 degrees Fahrenheit, 50 degrees Celsius.