I finally found the "line" applicable to Oil Level on my Stemco sight window devices. It is a circle in the clear plastic end of the bearing cover about 1/16th of an inch outside the edge of the red center plug, and I couldn't distinguish it from the plug expansion inside in regular daylight.
Both hubs are over full. Instructions say to add oil when the level gets down to 1/4" below the line.
instead of getting overly complex about rotating the hub (moving the vehicle, etc.), jacking a corner, employing theoretical methods of anti-gravitational back spin, chanting, rubbing the belly of a pregnant woman, etc.....
you can do what I just did- pull the red rubber plug. DUH
Some days we are like economists- you could line us all up end to end and we wouldn't reach a conclusion.