The McAdam ellipse is usually described by the order, which is the standard deviation. The first-order McAdam ellipse refers to the standard deviation of the color matching result change that is one time from the target color (see Figure 1). Similarly, the meaning of order 3, order 4, etc. If the two color coordinates fall within the first-order McAdam ellipse, the human eye can hardly see the difference between the two. The difference between the color corresponding to the boundary of order 3 McAdam's ellipse and the center color is the color difference that the human eye can detect. The McAdam ellipse of order 1 is very small. In most cases, what we see are scaled up McAdam ellipses, which are usually 7 or 10 times larger than the original ellipse. FIG. 2 shows the McAdam ellipse with a magnification of 7 times. Each ellipse in the figure represents the standard deviation of the color matching result with a change of 7 times relative to its central color point. This also means that the standard deviation between the two corresponding points on each side of the ellipse is actually 14 times greater.