Hello Charlie,
how very kind of you. It's not yours or Cathy's fault, it was quite clear from the article that you were trying to demystify a technical subject. It's just that when you are dealing with the lowest common denominator of technical understanding (that's me) you can't take a thing for granted. I was fine for the first few pages, great diagrams, understood the wandering pole etc. It was deviation that got me - not why it happens, but some of the terms. What is the azimuth, and I got confused about the significance of the shoreside range mark, which seemed to be a church. I got the adjustments OK, so I suppose all I'm really muddled about is a bit of the terminology and the exact significance of the shoreside range marks. If ever you want to run a future article passed the really stupid, I'm your girl....