It pays to have a second set of eyes looking at something. :-) Thanks for pointing out that repeated red fill update glitch.

As far as the slowdown problem goes, it dawned on me in my dreams last night that I wasn't cleaning up those items. I checked for memory gain, but there was none, so I let it go. But after switching to delay=1, I did see some sluggish performance after about 20 runs. I added the cleanup tags, and it seems to run fine now while holding down the spacebar.

I thought about creating the circle and arc as globals and just using hidden states to reuse them, but I thought I would show it created new in a sub, in case the tester wanted to randomly change the size and position of the circle on each run( which would be handy in a psychological test of eye movement).