PE, thx for the help.
The two test strips are from different days. From the very beginning, it took me like 10 test strips to calibrate the ColorStar. Then for each new day, I calibrate the Colorstar again. And it takes about 3 test strips to get it right subsequent days.
The test strips are supposed to be different, reflecting variations of the chemicals and any other changes (lamp, paper, etc). They can also tell me the changes of the chemicals.
Sry that I did not make it clear from the beginning.