A thermometer block reads the temperature of a Nuclear Reactor adjacent to it. It can be set to release a redstone signal when the temperature rises above a certain level, which is crucial in setting up an automated, safe Nuclear Reactor. By right-clicking on the reactor with a Wrench in hand, the Critical Temperature will be raised. If right-clicked with an empty hand, the Critical Temperature will be lowered. The Critical Temperature of the Thermometer is the temperature at which redstone signal is released if exceeded.