the trigonometric equations described hereinabove height measurement module 90 also operates when shaft s is installed in vessel v before the bottom end of shaft s or its paddle p reaches its lowermost position within vessel v upper end portion 94 bb of upper arm 94 b of vertical plunger 94 is biased in its highest position above lower end portion 94 cb of lower arm 94 c this constitutes a zero reference position for vertical plunger 94 as shaft s is being lowered into vessel v paddle p makes contact with upper end portion 94 bb by the time shaft s reaches its final normal operating position paddle p will have urged upper end portion 94 bb downwardly towards lower end portion 94 cb against the biasing force of spring 98 as the code strip for vertical plunger 94 is fixedly mounted in recessed area 94 bc of upper arm 94 b the code strip moves downwardly by the same distance as upper end portion 94 bb this distance constitutes the displacement magnitude for vertical plunger 94 which is encoded by transducer 96 and a signal is sent to control display console 60 for further processing one way to derive or interpret the height of paddle p above lowermost point 19 of vessel v is to.