When selecting the temperature control fluid, attention must be paid to high thermal conductivity and low viscosity with regard to homogeneous temperature distribution. In addition, the liquid should be inert, have a low vapour pressure, should not decompose chemically, nor burn, and should maintain its properties over a wide temperature range. In practice, silicone oils are usually used. The temperature range lies between -45 °C and +300 °C, depending upon the design. The calibration baths are fitted with a temperature-controlled liquid tank with a usable depth of 200 mm. The maximum immersion depth for the test items of 200 mm reduces heat conduction errors and achieves smaller measurement uncertainties.