The easiest way is to look at the circles as guides only - that is what they are after all.
For accuracy always compare the measured xy value with the target value.
All that information is displayed within the Calibration Interface.
Its is then a simple matter to see if the measured value matches the target value.
The CIE xy diagram is also unable to show with any accuracy the circle targets as valid 'acceptable' areas.
They are, and can really only ever be 'guides'.
With the CIE uv graph it is potentially possible to make the target circles more accurate to a given 'percentage' value.
Will look at that.
Adding Kelvin curves really is no help with calibration, and will confuse the CIE display unnecessarily.
Mob Boss at Light Illusion