The difference between mean and apparent time —i.e.
the difference between the time as shown by a good clock and that
indicated by a sundial. The greatest difference is in November, at the
beginning of which month the sun is somewhat more than sixteen minutes
too slow. There are days in December, April, June, and September when
the sun and the clocks agree.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
