[′rō‚tād·iŋ vi′skäm·əd·ər ′vak·yəm ‚gāj] (engineering) Vacuum (reduced-pressure) measurement device in which the torque on a spinning armature is proportional to the viscosity (and the pressure) of the rarefied gas being measured; sensitive for absolute pressures of 1 millimeter of mercury (133.32 pascals), down to a few tens of micrometers.