A quantity or condition which is varied as a function of the actuating signal so as to change the value of the directly controlled variable.
Figure 2 - Block diagram of automatic control system (5-2-045) incorporating a closed loop (5-2-080)
Reference: ANSI (modified)
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM