When using Autosize lines to display the lengths of lines, if the line is scaled so that one inch represents one foot, the default display format is in feet and fractions of feet (for example, the default display for 6' 3" would be 6 1/4', while the default fraction-as-decimal display for 6' - 3 11/16" would be 6.6875').
To show the result in feet and inches (i.e. 6' 3" or 6' 3-11/16"), the Divisions in the Ruler dialog box must be set to a multiple of the number of standard divisions of both inches (i.e. 16) and feet (12), or 192. Perhaps the best way to do this is to set the scale at .25 inches to 1 foot, and set the number of divisions to 48.
See the online help under Autosize Line for instructions on implementing ruler changes for existing lines.