The pointer on a dial-type thermometer is moved by a:

The pointer on a dial-type thermometer is moved by a bimetal element. This type of thermometer utilizes two strips of different metals that expand at different rates when subjected to heat. As the temperature changes, the bimetallic strip curves in response to the differential expansion of the two metals. This curvature drives the pointer on the dial, which provides a visual indication of the temperature being measured.

Bimetal thermometers are commonly used in various applications due to their simplicity, durability, and ability to provide a direct, easily readable temperature output. They do not require external power sources or complicated electronics, making them reliable for many HVAC and refrigeration measurements.

For context, digital sensors and thermocouples operate on entirely different principles. Digital sensors typically involve electronic components for measurement and display, thus do not have a moving pointer like that found in dial-type thermometers. Thermocouples generate a voltage based on temperature differences; they do not utilize mechanical movement to display temperature readings. Likewise, a mercury column thermometer doesn't apply here since it indicates temperature via the expansion of mercury in a glass tube, not through a dial indicator.

Understanding how the bimetal element operates helps reinforce the fundamental principles of thermal expansion used in various temperature and HVAC applications.