An analemmatic sundial is a kind of horizontal sundial in which the shadow-casting object is vertical, and is moved depending on the date.

To use this unique type of sundial, you step right into it — you become the gnomon and your own shadow indicates the time! The hours are indicated by marker stones set into a large ellipse. The central part of the sundial is called a date scale and is marked off in the 12 months of the year.
A person using the sundial simply matches the current month with its location on the date scale, and stands at that spot with their back to the sun. Their shadow then falls across the hour stones and gives the time — with surprising accuracy!

The hour markers are cast with roman numerals in the traditional way for sundials. These along with the dates cale (month blocks) are simply set into the grass or gravel at ground level.

Our Sundial consists of a set of 38 blocks:
A central date scale made up of 10 blocks (May/June and November/December being in the same blocks)
An outer ring of 12 number blocks for GMT reading.
An inner ring of 16 number blocks for BST reading.

As with all sundials, the layout of the components must be made to its own site Latitude & Longitude  -  since otherwise it would not be able to tell correct clock time, for your location. Providing it is set-out by following all the measurements and Instructions in the customised plans provided, then it should indicate the correct 'clock' time all year round.

Further Information:
The analemmatic sundial was probably invented some time between 1532 and 1640 by the 18th century astronomer J.J. de Lalande. He was born in Bourg-en-Bresse, France,near the church of Brou, on whose grounds is found the oldest analemmatic sundial in existence. In 1756 he was concerned that the dial was deteriorating, so he had it reconstructed in stone at his own expense.

The dictionary explaination: