What is viewing cone?

The viewing cone is the maximum viewing angle range that the display can either support a
minimum contrast value, or not become inverted. For example, a monochrome display might
support a contrast ratio of 2:1 minimum when viewed at 45 degrees from perpendicular in every
direction around the display. Beyond 45 degrees, the contrast will dip below 2:1. Often these
cones are not perfectly symmetrical.