David Runham (Letters, October 31) is under the misapprehension that sunrise and sunset are always symmetrical relative to noon, as defined by our clocks.

In fact, in mid February, time by our clocks is about 15 minutes ahead of time, as shown on a sundial.

Conversely, at the end of October, clocks are about 15 minutes behind sundial time.

This explains the logic of the dates chosen for the start and finish of British Summer Time.

Putting clocks forward in mid February would result in sunrise occurring almost half an hour later (clock time) than on the equivalent date (relative to the equinoxes) at the end of October.

Darkness in the morning is reckoned to be more undesirable, for safety reasons, than in the evening.

Time, as shown by clocks and sundials, is concurrent on four days each year, one of which happens to be Christmas Day. Look up ‘Equation of Time’ on Wikepedia.

Matthew Zepler, Southampton.