The 6/10 was subjective. If I draw an imaginary horizontal diameter across the lens, the upper part was sharp within 90% of the radius. The lower part was sharp to about 75%. Overall I would therefore estimate 80% of what is seen is sharp with 80% referring to the radius.
I am certainly not an expert here. Hope my 2c will be useful.
The only optics I can compare the 828 to is my Swarovski AT80HD spotting scope. Ratings are relative to experience with the scope. 1st rating is binoculars, 2nd rating is scope
Resolution - 7/10 vs 9/10
Portability - 9/10 vs 7/10...