Zodiac signs on the Balmoral sundial

This sundial was in the garden of Balmoral Castle. I was interested that it had the odd cross-hatch pattern on it and zodiac signs round the outside. Turns out that the curves going laterally across the sundial are the loci of the shadow of the tip of the gnomon. The shadow length will be different in different seasons. Thus the shadow length can be linked to a zodiac sign, which in this case is used to denote where the Earth has reached on its orbit around the Sun. I guess that you have to know whether you are before or after midsummer to select which of the two signs offered at the opposite ends of the curve.