Datacolor Spyder3 Elite Help Manual page 92

Phosphors
These values show the chromaticity values, in CIE xy, measured on the monitor when
full Red, Green and Blue samples are displayed. The values are stored, after chromatic
adaptation, in the ICC profile for the monitor. Applications will use these values as the
basis for their transformations of colors to be displayed on the monitor.
Delta E
White Point
This is a measure of how close the calibrated White Point is to the desired or target
White Point value. In Measured Luminance mode this is calculated as the
difference in Luv color space between the Target and Calibrated values for White
Point and White Luminance. In Visual Luminance mode this is not really Delta E
but Delta uv because it is calculated only as the difference in uv chromaticity (because
there is no numeric luminance target in Visual Luminance mode).
A Delta E of less than 3 is good. Less than 2 is quite good. Less than 1 is excellent but
not often achieved in practice (if you get Delta E less than 1, consider taking a trip to
Las Vegas).
50% Gray
This is simply an informative item that provides an indication of how well the
calibrated monitor is tracking gray chromaticity. This is an indication of the gray
tracking of the monitor hardware. The value is calculated as the difference in uv
chromaticity between a reading of 128 gray and the Target White Point. As such it is
not really Delta E but actually Delta uv (there being no luminance target for gray).
Determining Target Luminance Values
When setting the desired calibration values, the user can specify that Luminance
Mode is either Visual or Measured. The difference between these two modes is in
how the user is instructed to set the Black and White Luminance levels during the
Calibration process.
For most users, Visual mode is recommended. If you want to use Measured mode
then read on because you must first determine the Target Luminance Values.