I use online chess tactics problems to assess how good my brain is that day. I estimate there's a 300+ ELO variance, perhaps even more, in my performance between when I'm tired and when I'm rested.
300 ELO points between 2 players means that the higher rates one wins about 9 out of 10 games against the lower rates one. A huge difference in performance.
300 ELO points between 2 players means that the higher rates one wins about 9 out of 10 games against the lower rates one. A huge difference in performance.