The ornamental design for a ruler, as shown and described.
The fileof this patent contains at least one drawing/photograph exectued in color. Copies of this patent with color drawing(s)/Photograph(s) will be provided by the Office upon request and payment of the necessary fee
FIG. 1 is a front plan view, in color, of a ruler showing my new design;
FIG. 2 is a rear plan view thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a rear elevational view thereof;
FIG. 5 is a right side elevational view thereof; and,