Akai LCT2715 Service Manual page 71

Note (7) Definition of White Variation (δW):
Measure the luminance of gray level 255 at 5 points
δW = Maximum [L (1), L (2), L (3), L (4), L (5)] / Minimum [L (1), L (2), L (3), L (4), L (5)]
W
D/4
W/4 1
W/2
3W/4 3
Horizontal Line
D
D/2 3D/4
2
5
4
Active Area
25
: Test Point
X
X=1 to 5