19/20. The first many were very obvious. I missed #14 and I think right around there I started to slow down because the differences were getting smaller. Lookin

19/20. The first many were very obvious. I missed #14 and I think right around there I started to slow down because the differences were getting smaller. Looking away and then coming back helped, I think. It seemed like if you look at them too long, whichever circle you're looking at seems to shift color and it becomes really hard to discern the difference.