What is the name for a device that measures the rate of rotation of a revolving shaft?
Tachometer Tachometer A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute (RPM) on a calibrated analogue dial, but digital displays are increasingly common. The word comes from Greek "ταχος" ("tachos" "speed") and "metron" ("measure"). Essentially the words tachometer and speedometer have identical meaning: a device that measures speed. It is by arbitrary convention that in the automotive world one is used for engine and the other for vehicle speed. In formal engineering nomenclature, more precise terms
Revolving door Revolving door A revolving door typically consists of three or four doors that hang on a central shaft and rotate around a vertical axis within a cylindrical enclosure. Revolving doors are energy efficient as they prevent drafts (acting as an airlock), thus decreasing the loss of heating or cooling for the building. At the same time, revolving doors allow large numbers of people to pass in and out. Around the central shaft of the revolving door, there are usually three or four panels called "wings" or "leaves." Large diameter revolving doors can accommodate strollers and wheeled luggage racks. The tallest