The fluid always seems to creap way up one side. I have always figured that one side is flat against the oily lower tube. View the stick on both sides and use the lower one, it will be accurate.
There also will be a significant difference between cold and hot. The testing should be done hot, but once the relationship is learned for your trannie good info can be had cold, running.
Bosch Master, ASE Master, L1
33 years MB technician