Mass dials

This type of medieval sundial is most often found on the south side of churches, on their walls, buttresses, windows and doorways. They are usually about a hand span in diameter and are often at shoulder height or less. A horizontal rod gnomon set into a hole in the stone block or the joint between two stones would have cast the shadow.

These dials may be just a few radiating lines or many, a ring of dots or within scribed circles or semi circles.

They are called Mass dials because it is thought that some showed the time of the Mass and other services held during the day. They are also known as scratch dials because many of these dials are more scratched than carved into the stone.

These dials showed 'hours' that were not equal in length throughout the day and the year. They are not mathematically correct and many are best described as 'event markers'.

Fixed dials

By the C15th modern sundials were being made in Europe. These are based on scientific principles and are the sorts of dials most of us are familiar with today.

Fixed dials are usually found on walls, pillars and pedestals. They are mathematically correct and show hours of equal length throughout the day and year. Their gnomons are usually sloped (polar aligned) and they are made in a great variety of forms, shapes and sizes.

The time they show can easily be converted to clock time by using an Equation of Time chart and allowing for longitude.