From TDN

The Values box shows coordinates based on where your mouse is in the the X, Y, and Z axis. If your mouse is not inside one of the screens no coordinates will be shown.

The coordinates detail is based on the Grid Spacing (if your Grid Spacing is set to 0.25 then the numbers will be displayed in increments of 0.25, for example: 1, 1.25, 1.50, 1.75, 2 and so on), which can be changed under the Properties window/Prefs.