As is generally known to navigators (though the statement surprises most laymen) the Sun is a poor timekeeper; rated against its own average behaviour, it is over 14 minutes slow in mid-February, over 16 minutes fast in early November, and more than 5 minutes wrong, one way or the other, on more than half of all the days in the year. The ‘errors’ are however very nearly the same from year to year; the principal variation is a slight oscillation in phase due to the incidence of leap-years and the effect of this is too small to be detected on a sundial, where the accuracy is limited to about the nearest minute by the Sun's apparent diameter however large or small the dial may be. It is thus possible to make a table of the ‘errors’ (i.e. of the ‘Equation of Time’), say for every tenth day and to the nearest minute only, and to engrave it permanently on the dial, leaving the observer to interpolate to the actual date and add or subtract the correction. Provided the table includes also the allowance for the longitude-difference from the standard meridian of the zone, the result (if the observer does his arithmetic correctly) will be standard time for that zone. But it is quite possible to save the observer this labour.