The original idea was to put a target on the screen to make it simple for a person following the SMPTE ST 196M-2003 Standard to make a consistent measurement (which says: "Luminance of the screen sides and corners shall be measured at a distance of 5% of the screen width from the screen edges...") That means that a person in the proper place in the auditorium could/would/should shoot...or aim to shoot...at different designated spots on the screen, 5% in from the edges and corners.
And because a solid white screen has a lot of glare, a dot was specified in the Study Group instead of a completely white screen, so that measuring tools could minimize the glare.
Another concept that was incorporated was that a long room might need a large dot - specifically a 20% of height dot instead of a 10% dot so that any room that was too long could give the measuring person an excellent chance of getting only white in their tool's 2° measuring spot. To accomodate that, the positioning line was placed 15% in from the edges, thus a 20 percent dot could sit on the 5% edge of the screen.
Then, allowing for simplicity, the smaller dot should be on the same line that was indented 15% in...because...who knows. Except that you can't measure the reading of white at 5% from the edge of the screen.
So, that is why you should remember that these are only for testing, not real live finished products. And, remember: these are 2020 4K 16 bit TIFFs.
Quality Assurance Tools and News for Cinema Exhibition
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