In short: green is Glicko2, red is OGS.
In more detail:
The green line is a OGS like Glicko2 calculation. With OGS like I mean, I use the current rating of the opponents, not their rating at the start of the rating period (base rating).
For the red line, I had to artificially raise the deviation of the players base rating at the start of each rating period. I use the deviation provided by OGSs termination-api for the first game of the new rating periode, because I don’t know how they get calculated by OGS (as far as I can tell, it’s an undocumented feature of the OGS rating system).
For both lines I use:
- rating period = 15 games or 30 days (30 days never applies in this special case)
- initial player rating = 1500, deviation = 350, volatility = 0.06 (that’s what OGS uses)
- τ = 0.6 (τ=0.3 or τ=1.2 could I’ve choose as well, they cause no visible difference in my tests)
- For the current rating of the opponents I pull their rating history and look up their rating 1sec before the “current” rating calculation.
I want to note that after approx 45 games, the deviation doesn’t get lower anymore. It’s always between ≈90 at the start of a rating period, and ≈65 at the end of a rating period. This is a feature common to almost all players on OGS, playing multiple games per month, as you can easily verify here: OGS rank histogram (outdated) - #28 by DVbS78rkR7NVe
Glicko2 deviation drops below 34 at the end.