A rotary switch which alternately charges a fixed capacitor from a constant d.c. voltage source and discharges it through a fixed resistor. The average current through the resistor is proportional to the speed of rotation of the switch.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
Centre of buoyancy
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM