I claim the ornamental design for a calculator, as shown and described.
FIG. 1 is a perspective view of a calculator, showing my new design;
FIG. 2 is a top plan view of the invention;
FIG. 3 is a bottom plan view of the invention;
FIG. 4 is a left-side elevational view of the invention, the right-side elevational view being a mirror image thereof; and,
FIG. 5 is a front elevational view of the invention, the rear elevational view being a mirror image thereof.
The thick broken lines in FIGS. 3–5 define the bounds of the claimed design, within which is illustrated environmental matter in thin broken lines that forms no part of the claimed design.