While there was improvement with practice with the dominant hand, the weak hand did not improve enough to determine if the change was relevant. I tried to vary how long I waited to drop the ruler, as I could see my partner trying to time my release. In conclusion, I think if the ruler catcher simply tries to catch the ruler and not time the release of his/her partner, the results would be very consistent without much improvement with practice.
I think there was a slight improvement, at least shown by my data. Either way, the change shows humans improve and are inconsistent and therefore not machines.