FIG. 1 is front, right and bottom perspective view of an operating knob for portable electronic computer showing our new design;

FIG. 2 is rear, left and top perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a top plan view thereof;

FIG. 6 is a bottom plan view thereof;

FIG. 7 is a left side view thereof;

FIG. 8 is a right side view thereof; and,

FIG. 9 is a reference perspective view showing the operating knob attached to a portable electronic computer.

The subject matter in FIG. 9 shown in broken-line format is for environmental purposes only and forms no part of the claimed design.