The measuring system of the dial thermometer consists of a stem, capillary and Bourdon tube in the casing. These parts are combined to form a single unit. The entire measuring system is filled with an inert gas under pressure. A change in temperature will cause a change in internal pressure in the stem. The pressure deforms the measuring spring and the deflection is transferred to the pointer via a dial movement. Fluctuations in ambient temperature affecting the casing can be neglected, as a bimetal compensation element is fitted between the dial movement and the measuring spring. The scale ranges are between -200 and +700 °C with an accuracy class 1 in accordance with EN 13190. You find further information in the video below: Bimetal vs. gas-actuated thermometers