Article of the month December

Bury St. Edmunds Curve

On a pillar in Bury St Edmunds, England, there is a cube sundial from 1870.
The actual sundial is on the south face of the cube, and on the east face a short text is inscribed.
But in this "Article of the month", we are more interested in the curve displayed on the west face.
This curve is visible in the second photograph.

This graph for the equation of time today is known as the "Bury St. Edmunds Curve".
Along the horizontal axis is a linear scale for the equation of time.
The date scale, however, is not along the other axis, but is plotted along the curve itself.
This is done in such a manner that the distance on the curve between the points for any two subsequent days is constant.

The date scale begins with 1 December in the top left, and runs clockwise.
At any point of the curve, the drawing direction may be reversed, so many variations are possible.
The end point of the date scale is below the starting point, but the curve remains open.

The same curve, drawn by Kevin Karney, is shown below, except that here the date scale begins in the lower left, and runs counter-clockwise.

Finally a closed graph, also by Kevin Karney, is shown.
On his website there are still more variations on this curve.