What rating PFF considers "average"

[*ochocincos*]

I know that while we talk about performance of players, especially ones who don't accumulate statistics, some of us reference PFF.
However, it can be a little difficult to determine what is considered average and above/below.

Luckily, PFF_Bengals Twitter has directly stated what "average" should be - 60.0.

Pass-blocking grades from the #Bengals loss to the WFT (60 being average):

Jonah Williams: 75.7
Hakeem Adeniji: 59.8
Trey Hopkins: 50.4
Quinton Spain: 40.0
Michael Jordan: 23.5

— PFF CIN Bengals (@PFF_Bengals) November 23, 2020

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So what's the rest?
Below average - 50's
Good - 70's
Elite - 80's