The Clip On thermoregulator was invented by Techne in 1948. Thermoregulators are supposed to be used with Techne particularly unheated baths and other similar laboratory vessels. They will circulate and heat and at the same time control the temperature of any liquid in the bath within specific limits.
The TU-20HT in particular can work in temperatures between -40°C and 250°C. It offers a very stable working temperature. You can use the 1.8kW heater if you want to heat water faster. It has 4-digit display to show the temperature using LED digital display. You can take advantage of the RS232 connection for updates to the software package. It has an audible alarm and an adjustable temperature limit.