Gnomon Holes

[Mike Cowham]

I have just been asked the question to which I thought I knew the answer, but now I am not so sure. On English horizontal dials there are frequently two small holes drilled in the dial plate at the point where the root of the gnomon contacts the plate.  The question is, 'What were the holes used for?'  I understood it to be an aid for alignment of the gnomon but now I believe that these holes could have been used to take a pin or point of a compass/dividers during marking out.  Perhaps some of you who still make such dials will use a similar method? Regards, Mike Cowham Cambridge UK