Currently, -kyu/-dan ranks (hereinafter “grades”) are given directly based on the Glicko-2 rating, with a simple cutoff between the grades. This is fine, but it's common for ratings to fluctuate. If they fluctuate around the cutoff, the player will quickly lose and gain the grade over and over. I would say this is undesirable.
An easy fix to this is to implement a buffer between the grades, where if you fall below the cutoff, there's a buffer before you lose the grade. Since new grades are given every 75 rating points, there could be a buffer of perhaps 25, 50, or 75 points.
For example, with a 50-point buffer, if a player reaches 1550, they gain 1-dan. If they then fall down to 1542, they don't lose 1-dan. Only when they fall below 1500 do they grade down to 1-kyu. As an edge case, if they fall straight down to 1474, even though that's below the cutoff for 1-kyu, they still only fall to 1-kyu, since it's within the buffer.
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