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In article <[log in to unmask]>, Hilary Curtis <[log in to unmask]> writes > >>I thought all centuries were not leap years but milleniums are. Are there >>other variations? > >No. The divisibility by 400 rule gives a pretty good approximation to >the true length of the earth's orbit round the sun. Nowadays, they add >in occasional leap seconds whenever any further correction is needed, >rather than complicating the leap year formula. > The situation is a little more complicated than this :) You are right about the division by 400 rule, all this is to do with the length of the year expressed in days. On the other hand leap seconds correct for the errors in the length of the day ( ie the earth's rotatation not revolution). The changes are administered by a woman in France who heads the "International Earth Rotation Service" (I kid you not!). Obviously the woman who makes the world go round :-) -- Mike Rushton %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%