Also known as Mass Dials, these were a very early and primitive form of sun dial.
They were used by priests to advertise the time of the next service.
Usually in the form of a semi circle about ten inches across, they were scratched into the south wall of the church.
A hole was bored at the centre and a number of lines scratched from the hole to the arc.
The priest would place a short stick in the hole and when the sun shone the shadow of the stick on to one of the lines, the next service would start.
(text and images courtesy of Heritage Inspired)