The chart shows the display’s color fidelity. The RGB color values coming from the graphics card’s output are supposed to match as accurately as possible the values the monitor actually displays. Identical color values for RGB (i.e. red = 128, green = 128 and blue = 128) always result in a shade of grey. The grey tone coming from the graphics card’s output is supposed to match as much as possible the grey shade shown on the monitor. Thus, a straight line where the three RGB colors are congruent with each other would be the ideal result in color fidelity.