This picture was taken shortly after the unveiling ceremony, and shows how the dial is positioned.
The meridian of 2 degrees longitude west passes through the town hall, and the dial is compensated for the 8 minutes discrepancy between local and Greenwich mean time.
The dial is not direct south facing, but is rotated one degree from south facing towards the east.
The slate dial was made by Letter Cutter John Shaw, and the dial calculations were carried out using the vertical sundial
Calculator that is part of this web site.
Normally the values input to the calculator to obtain the dial shadow angle markings are 15 (degrees) for each hour, (1pm=15, 2pm=30 etc).
As the longitude is 2 degrees west, the input values were adjusted as follows:- For the west (am) face 2 was added to the angles, so the hours were input as 17, 32, 47 etc, and for the east (pm) face the input values were 13, 28, 43 etc.
The effect being to rotate all the hour shadow angles clockwise to compensate for the 8 minute longitude effect.
The calculations also accounted for the fact that the dial is rotated from south facing by inputs of 89 and 91 for the gnomon side angles.