The discussion of Rotation Period and Day Length presumes that the motion of the planets around the Sun is more or less uniform. Because Mars' orbit has an eccentricity of nearly 10%, its angular motion around the Sun varies by as much as 20%, which can alter the difference between the length of the day and the length of the rotation period, normally around 2 minutes and 12 seconds, by about half a minute. This means that in a week or so, at certain times of the year, a uniform clock will run several minutes ahead or behind the rotation of the planet. The effect is similar to the one which makes sundials run "fast" or "slow" on the Earth, but is considerably more exaggerated.