The cruciform stone has four concave sides leaving four curving arms between them, thus creating the cross shape. This particular stone has a small concave end on each curving arm [not visible in the photo]. So the single stone has eight dials, on four large concave sides and four small ones. [Note: the shadow in this photo is from indoor lighting not from the sun.]
The stone is beautifully carved and by the same hand as its companion globe stone. The graduations are hour, half hour, and quarter hour lines, and ten minute points. In the view shown in the photo, the morning hours are above from 7am to 11am, while the afternoon hours are below from 1pm to 4pm. The hours will read correctly when the stone is in position lying parallel to earth’s equator.
A lectern type of sundial is often complex. An excellent example from the 17th century at Woodhouselee near Edinburgh is held by National Museums Scotland. A cruciform stone on a lectern sundial will need to fit into the complex design, particularly for size. The cruciform stone described here seems too big to fit a lectern, and its origins and mounting details are unclear.