The dials were carved into the walls of some churches and monastic buildings
A new discovery at an island abbey in the Firth of Forth has revealed the Augustinian canons who once lived there measured time using a mass dial.
Conservationists working at Inchcolm Island found the remnants of a special sundial which they believe may have been carved into a wall.
Until now mystery has surrounded the method used by the order to tell time.
While well-known in England, the British Sundial Society said there were relatively few dials in Scotland.
Historians believe the Augustinian canons lived according to a strict routine, which made it essential everyone in the community did the right thing at the right time.
The dial at Inchcolm, which has been broken in two, was discovered by Historic Scotland collections registrar Hugh Morrison and medieval stones expert Mary Markus.
They were carrying out preparatory work for a project to examine and catalogue a collection of about 50 pieces of carved medieval stone being kept at the abbey but which were never studied.
Mr Morrison said: "While sorting through the stones I found a fragment with distinctive radial markings carved on it that reminded me of mass dials that I had seen on churches in Gloucestershire.
"In a separate location I turned over another stone and was really pleased to discover that it fitted together with the other half of the mass dial.
"Better still, it still has the corroded stub of the iron gnomon which would have once cast its shadow along the radial markings of the dial."
Mr Morrison said he was hopeful his team would be able to discover the original location of the dial on the south side of the abbey.
He added: "Medieval timekeeping was very different from our present day dependency on the accurate measurement of time for catching trains, getting to work or viewing TV programs.
"Changing seasons and weather meant that mass dials could not always be used but when the sun shone they provided a relative means of coordinating community activities."