The ornamental design for a portion of a clock, as shown and described.
FIG. 1 is a front perspective view of a portion of a clock showing a first embodiment of the new design;
FIG. 2 is a front view of FIG. 1;
FIG. 3 is a right side view of FIG. 1, the left side, top, and bottom views being substantial mirror images thereof;
FIG. 4 is a front perspective view of a portion of a clock, showing an alternative embodiment of the new design;
FIG. 5 is a front view of FIG. 4; and,
FIG. 6 is a right side view of FIG. 4; the left side, top, and bottom views being substantial mirror images thereof.
The unshown rear of the clock forms no part of the claimed design. The broken line showing of alphanumeric characters in FIGS. 1-2 and 4-5 and the unshaded areas therein, are for illustrative purposes only and form no part of the claimed design.