Sundial of the month October

I first saw this sundial in 1982 in the London Science Museum.

Curious as I was, I wrote to the maker for more details.
W.G. Benoy from Newark, Notts, in the United Kingdom designed and made this sundial.
The design contains an element that hardly any other sundial has.
Usually a shadow (line) on a dial face indicates time, but here, time is shown by an arrow of (sun) light.
Fittingly, the designer calls this an 'optical sundial'.

The dial face is in the equatorial plane, because of which the sundial will only function in spring and summer.
Because Summer Time (DST) is in force nearly that whole period, that is what the dial shows.

In the centre there is a round glass vessel filled with water. The axis of this cylinder points towards the celestial pole and is therefore parallel to the axis of the earth.
Such a vessel automatically forms an arrow of sunlight in its own shade. Try it with an emptied jam jar filled with water. It could hardly be simpler.

As far as I know, this sundial is unique in its kind in the Netherlands.
I enjoy its presence on my terrace every summer.

J.G.T.M. Taudin Chabot