Fast ... methinks I'll go double check those mast base connections.
NightOwl - you are absolutely correct. That is what it says but I was uncertain whether that was procedure for recalibration or only for calibration on new installation. I'll check it out again on the weekend.
Thanks for all the advice.
“Give a man a fire and he's warm for a day, but set fire to him and he's warm for the rest of his life.” Terry Pratchett