Description: Period of time from the commissioning of a plant, part of a plant, a component or a line system; Name: service life
Description: passed time period after comissioning of a system, sub-system, component or piping; Name: Operating time 
Description: variable quantity, which is not influenced by the control but is introduced into the control system from outside with the aim of making the final controlled variable follow it in a given relationship; Name: command variable