Originally Posted by
pontifex
The compass was original and not accurate to within 20 degrees mostly.
I had to swing that compass once when it came out of the shed. It was miles out and the corrections just did not work. The East-West/2 to give an average correction didn't work.
Had the error on east been 3 degrees left and west 3 degrees right then the correction of 1.5 would have been OK. The reading on east was actually 60 degrees in error one way and on west of the same order so that the correction was about 1 degree but did nowt for the compasses.
The error of course was trying to apply basic compass swing methology to a compass that was grossly inaccurate. This Jengo wandered up and asked how I was getting on. Not very well. I explained the problem an dhe asked if I had tried a Sperry swing. No.
He explained it and I followed that procedure and our final accuracy was well under 5 degrees.