Mass Dials

18th century mass dial at Boxgrove

How did the vicar know when to start services in the days before clocks and watches? They would consult a sundial called a mass dial or scratch dial inscribed on the south wall of the church.

Mass dial now inside Bosham church, believed to be Saxon

In Saxon times, mass dials were often sophisticated timepieces, carved in relief, but after the Conquest they became much more home-made and functional - just a horizontal gnomon and holes or scratches in the stone where the shadow would fall at the start of services. 

The diagram shows a Norman scratch dial at Ashton-under-Hill, Worcestershire. The hole in the middle would have held the wooden gnomon, which would have been replaced periodically as they rotted away. The scratches mark noon and morning and evening services.

Some mass dials were even simpler. The priest would use the gnomon to bore a hole in the soft mortar between the stone joints, and a horizontal line of holes in the stone below to show the times.
Later mass dials became more elaborate and elegantly carved, with regular radiating rays and semicircular arcs, looking a bit like a school protractor. Some are complete circles, despite the fact that the upper half was just for show.

Mass dial at Wiggonholt

In the 18th century, mass dials with corrections for the time of year and complete with Roman numerals appeared, but clocks were appearing in churches by that time so it may be that such advanced dials were more of a hobby of the rector rather than necessary for timekeeping.
Mass dials are usually found on the south corner of the chancel or on a buttress, but many have been moved in the course of restoration, some even to a north wall where they would be completely useless!