(This item pertains to the check boxes on the General tab of the Setup Options dialog box. You can open it through the F5 key or through the Edit | Preferences | Setup menu option.)
This check box sets the default value for the Gap Only check box used in new Location dimensions for the current measurement routine.
If you select Gap Only then, when the measurement routine next starts, the GAPONLY/ON command gets added into the Edit window. In addition, the Feature Location dialog box (Insert | Dimensions | Location) for Location dimensions automatically has its Gap Only check box selected by default whenever you create a new Location dimension.
If you deselect Gap Only then the Feature Location dialog box has its Gap Only check box also deselected whenever you create a new Location dimension.