The measurement can be done with a test image which has 11 gray value steps (from 0% to 100% with 10% distance between two steps). The image generated with the KowoDisplayTest program can be used - the boxes with the gray value steps are marked with their percentage.
With the Kowotest Densorapid DL the luminance at the desired step can be measured. The results shall be in a table like this example


and the deviation to the GDSF shall be calculated.