The MacAdam Ellipse is applied in the CIE Chromatic Diagram. I understand that humans distinguish some colors better then other colors (that's why the shape is eliptic / a horseshoe / inverted U-shape), and that the diagram is used to check wheter a specific color space is in or out of gamut.
The highest used y value is 0.84 (the top side of the ellipse ... it respresents 520 nanometers, green).
The lowest x value is 0.0 (the left bottom side of the ellipse ... it represents 380 nanometers, blue). And, on the right, at the coordinates: x 0.73, y 0.64, the red hue 680nm is displayed.
What I don't understand:
Why is this diagram non linear?
Why is the highest y value 0.84 and not just at y = 1.0?
How was the CIE Chromatic Diagram "derived"?