The ornamental design for a back cover of a watch with a variablepattern, as shown and described.
FIG. 1 is a top surface of my new and ornamental design for a back cover of
a watch having a variable pattern in which the bars extend radially from a
central portion. When the watch is moved, the underlying mechanism causes
the design formed by the bars to vary irregularly in number, width, and
spacing. The watch case does not form part of the claimed design. The
design is comprised solely of the back cover. The particular watch case is
shown only as environment.
FIG. 2 is a top surface view showing a second variable pattern; and,
FIG. 3 is a top surface view showing a third variable pattern.