Until clocks started to become common in the late middle ages, the sundial was the most usual means of keeping time in Europe. And the most normal reason for needing to know the time was in order to be able to attend church services regularly and on time. As a result, many churches had sundials mounted on their walls to assist the priest and his flock in keeping to the timetable.

In Britain today there are 1,965 remaining vertically-fixed sundials, according to the British Sundial Society. Of these, 60 per cent are attached to the walls of churches, priories or other ecclesiastical buildings.

The decline of the sundial has been a gradual process: it was not until the end of the 19th century that the French railways gave up their practice of regulating train times by means of sundials - a curious fact considering that in most places it was the arrival of the railway that provided the first practicable method of standardising time across a whole country.

A drawback of the sundial as compared with the clock is that as sundial indicates what is known as Local Apparent Time. The time indicated will differ from one place to another, often by many minutes, because of the difference in the time of sunrise depending on how far east or west of a given point the sundial is. But the time indicated by a sundial will also vary according to the time of year. The earth does not orbit around the sun at a constant rate, and the inclination of the earth's axis to the plane of its orbit also means sundials will give slightly different times at different times of year. This sort of problem can easily be corrected, however, by adding or subtracting a set amount of time from the sundial's reading according to the location or the time of year. Some sundials are made with mechanisms that allow the gnomon, or pointer, or sometimes the whole sundial, to be moved to the correct position.

Many people are attracted to this ancient, if unexpectedly complex, method of telling the time. Gardeners in particular seem to prize the old fashioned charm conferred by placing a stone sundial in the middle of their lawn. Other people go even further than this. The British Sundial Society is a group, currently numbering around 600 people, dedicated to the preservation and study of sundials. The Society emphasises its role as an educational organisation, and encourages schools to study the sundial and the theory that underlies its use. The study of sundials has even been incorporated officially into the national curriculum.