The ornamental design for a cover of scale, as shown and described.
FIG. 1 is a perspective view of a cover of scale in accordance with the present invention;
FIG. 2 is a front view of a cover of scale thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left view thereof;
FIG. 5 is a right view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The features shown in broken lines in the various Figures are for illustrating environmental structure and form no part of the claimed design. The surfaces of the cover of scale are not limited to any color designations.