He's using CIRCLE 220-I, 145-I (Line 100), i.e. adjusting the center position.
CIRCLE definitively works fine, I'm using it in MEGABomb for explosions, and they grow centered as intended.
Viewing post in a most BASIC card jam comments
Oh, sorry, I meant something else: Look at the left side and the right side of each circle. The right side looks a little more pointy, doesn't it? It's not the same as on the left. MEGABomb shows the same problem, just smaller, due to the resolution. It's just about few pixels.
There is also a difference between ROM-versions, with 920413 being particularly spiky, not circle-like at all. I'll test this some more later, and maybe open a bug report. Thanks for pointing at MEGABomb as second test case, I didn't notice it there :-)