Thermocups and cup heaters are designed for controlling the tem-perature of a mud sample while taking readings with a rheometer or viscometer. Normal heat-up time is 15 minutes. Drilling fluid has a low thermal conductivity, so it must be agitated in order to reach a uniform temperature within a reasonable length of time. For safety considerations, the fluid should never be heated above 200°F (93°C). The rotor and bob should not be immersed for long periods in the fluid as vapors will rise up into the bearings and con-dense, causing corrosion. The holes in the stage of the OFITE Viscometers have been positioned to hold the heated cups at a 45° angle to the line of the instrument for better accommodation of thermometers and power cables