Click the Office Button and choose Word Options. Select the Advanced category and, in the Editing options section, select the Keep track of formatting checkbox. Select the Mark formatting inconsistencies checkbox. Click OK.
Another way to see this difference is to notice that, relative to the stars, the Sun appears to move around Earth once per year. Therefore, there is one fewer solar day per year than there are sidereal days.
What the previous three answerers said is correct. Calculating the solar day from the year and the sidereal day is one of those synodic period kind of jobs. solar day = 1 / [ 1 / (sidereal day) - 1 / year ] 86400 sec = 1 / [ 1 / (86164 sec) - 1 / (31556926 sec) ]