Fer de Vries contributed: > >It is not a good idea to wrap a south facing dial around a cylinder. >That will not work properly. >Any straight line on a plane southdial will change into a curved line on a >cylinder. >So you have to calculate more the 2 points to draw a line. > >For local suntime, with or without correction for latitude, a style parallel >to the earth axis may be used.
A laser trigon spaced at several locations on the style would fix a number of true points for interpolation. A word of warning. If making a laser trigon from a laser 'pointer' don't assume that the axis of the diode laser beam it contains is co-axial with the casing. In fact you can be almost certain that it is not. I had to overcome this problem and several others in making a trigon with a pivotting laser to mark out a dial on an irregular conical surface. Tony Moss.
