I'm getting quite a few questions about changes to rating values, mostly in the form of "why have my ratings changed?"
The short answer is - ratings have changed because 0.8.6 did a big artillery reshuffle.
Basically, most of the high-tier arties got raised a level or two in 0.8.6, so for people who played these SPGs their average tier went up. And because all the ratings use average tier information (some directly, some less directly), the ratings change from that (most by quite small values).
I have already adjusted Performance Rating a bit to compensate for that (for example, I removed the "average tier adjustment" of +2 tiers for SPGs that was there). Still I will check later on if more tweaks are needed.
For WN7 and ER I don't control these formulas so I will wait until their creators decide to change them (or decide to leave them as they are).
But in any case - these changes apply consistently to everyone, and I retro-fitted them to previous snapshots to avoid any strange "ratings jumps", so hopefully they don't cause much disruption.
P.S. Also, the biggest confusion is for servers where 0.8.6 is not applied yet, so they will see their t8 arties as t10 arties already in NoobMeter. Hopefully they get 0.8.6 soon and all is well again.
P.P.S. Creators of ER rating have declared they will not adjust the ER formula, but will adjust the way it is interpreted.