Sonnenuhr in Düsseldorf: Equation of time

Another great municipal sundial. Note that the angle of the gnomon is only 51 degrees because we are much further south. A correction curve has been provided. It explains that there is a discrepancy between Sun-time on a given day and what you ought to expect. In other words, it doesn't take exactly the expected 24 hours between noon on two consecutive days - ie the time when the Sun is highest in the sky. This is due to three considerations: 1. The orbit of the Sun is not a perfect circle and is a slight ellipse. 2. The axis of the Earth is tilted. 3. The Earth is not just rotating on the spot. Every day it goes on its orbit round the Sun a little bit further. I noticed that the correction curve given is different to the one I've seen before at Amble in Northumberland http://wigtonphysics.blogspot.co.uk/2014/08/time-in-amble.html So the correction must be location dependent. I have found this https://en.wikipedia.org/wiki/Equation_of_time which I hope to have time to understand soon.