Many Cooperative Observers use the Cotton Region Shelter (CRS) to record maximum and minimum temperature data.   A CRS is typically a wooden structure with louvered sides, a slotted bottom, and a solid top.   A CRS is usually made of pine, painted white, and sits atop a wooden or metal base 5 to 6 feet above the ground.   Some CRS's have an electric fan inside to allow for better circulation during light wind conditions (less than 5 mph) as thermometers often register too warm during light wind conditions.   This is especially true during the day in bright sunlight, although this may occur at night as well.

Thermometers used in a CRS are Liquid In Glass (LIG) and are either alcohol or mercury.   Alcohol thermometers are employed in the colder climates where winter temperatures drop below -40 degrees, the freezing point of mercury.   Minimum temperature thermometers have a small bar embedded in the liquid that is pulled down the tube as the temperature falls.   As the temperature warms again and the liquid moves back up the tube, the bar remains at the minimum temperature.   This allows the observer to read the lowest temperature.   Maximum thermometers have a small break near the base of the well of liquid at the bottom of the thermometer.   As the temperature falls from the maximum, this break in the liquid keeps the liquid in place at its high point.   The maximum and minimum thermometers are mounted on a rack.   After noting the highest and lowest temperatures, the observer then tilts the rack.   This resets the thermometers by rejoining the liquid in the "maximum" thermometer and sending the bar back to the top of the liquid in the "minimum" thermometer.   The thermometers are now reset, allowing observation of the highest and lowest temperatures for the next day.

Another and newer type of thermometer is the Maximum Minimum Temperature System (MMTS).   An MMTS is an electronic thermometer, not too different from the type one might buy at a local electronics store.   The MMTS is a thermistor.   This thermistor is housed in a shelter similar in appearance to a bee hive.   This design is similar in functionality to the CRS.   Currently, the MMTS requires a cable to connect the sensor with a display.   Future plans are for wireless displays.   This would eliminate many of the problems associated with cabled systems.