Why is February short? Why did eleven days vanish from September 1752? George Nichols Packer’s Our Calendar answers with the full arithmetic of civil time: solar years and lunar months, the Julian slippage, the Gregorian reform, dominical letters, and the venerable machinery for computing Easter.
It is a compact education in the mathematics hiding inside every date on the wall. Download the free EPUB and never again wonder why the calendar behaves the way it does.