A single directional thermostatic controller can maintain a constant temperature set point within an enclosure surrounded by a relatively constant ambient temperature. The set point tolerance is defined by a hysteresis range. Once the set point is achieved, the controller shuts off the Thermoelectric Cooler Assembly. When the control temperature changes to outside the hysteresis range, the controller turns on the thermoelectric cooler assembly and restarts the cooling mode process. This cycle continues until the controller is shut down. Refrigeration mode in an indoor environment is a good example of this where a narrow temperature swing can be tolerated. Proportional Controllers use proportional regulation to maintain a constant temperature with no swing in the control temperature. This is accomplished by using a PID algorithm to determine the output value and a Pulse Width Modulation (PWM) output to handle the physical control. Proportional Controllers are often used in heating and cooling systems where the temperature must stay constant with no change regardless of the change in ambient temperature. The PR-59 is mountable at the system level and comes with software to connect it to a personal computer. Settings can be adjusted while the thermoelectric cooler assembly is running which is beneficial for product development. A Bi-Directional Thermostatic Controller operates in the same manner as a Single directional controller except the output can operate in both heating and cooling modes. Controllers with a Bi-Directional Output are used for maintaining a constant temperature within an enclosure surrounded by an ambient environment with a much larger temperature swing. Outdoor kiosks are a good example of this.