Michael TLV writes:

• The Chromaticity Triangle is now clearly shown on the scatter graph. The points within the triangle are all the colours that the NTSC television system can display. This makes it easier to describe to the client about the coordinate limits.

• A small circle called “Close” has been incorporated into the graph. It roughly shows anyone looking at the graph the visual significance of the calibration work. It is a compromise and a simplification that gives the user a rough idea about their grayscale accuracy. If the pre-calibration readings are all located within this circled area in addition to the post-calibration readings, then the likelihood of the client noticing any visual difference is small. (i.e. Most people probably cannot tell the difference.)
  
  If the pre-calibration readings are located outside of the circle, the before and after differences in the grayscale should be obvious to most people. This is a simplification at best because the human eye is actually more sensitive to changes in the grayscale at lower light levels like the 20/30/40 IRE range compared to 90/100 IRE. The eye is also more sensitive to certain colours like green and red hence the slight shift of the circle toward the blue end. Much more blue is required in the grayscale before we can notice a change. The actual shape of the perception range is more elliptical than the circle shown on the scatter graph.

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