ABSTRACT
Sundials measure time as it is, based on the idea that a day is the time between two successive noons. It is not equivalent to ‘clock time’, which assumes that each day is exactly 24 hours long. The length of a day varies slightly throughout the year, i.e. the length of time between the noons, when the sun reaches its highest point (when it crosses the meridian). Sundials take the days as they are, varying in length from 23 hours and 59 minutes and 29 seconds on 25 December and 24 hours and 19 seconds on 1 September.
