Each machine of a certain dimension has, either because the legislature prescribes or for operational reasons, a local speed display. For many years, Horn-eddy-current tachometers have met all requirements in terms of display accuracy, robustness and maintenance and come in a variety of scales diameters. Even today, these devices are attached to machines without external power supply.
Almost all in practice occurring connections can be realized by appropriate design of the connection part. The versions with angled drive can optionally operate dependent or independent of turning direction.