Dipstick For Auto Transmission, how do you tell full?
 

We have a 2000 Chevy Duramax Diesel HD 2500 Crew Cab but when we check our transmission it is not easy to tell where the full line is. We do not have a manual or anything and there are 3 different areas on the end of the dipstick which are etched but we have no idea where the full line is supposed to be.
Any help will be appreciated!