Moving the mouse in a circle shape very slowly will result in the mouse pointer moving in a rectangular fashion.
@Thorham -
I tried really hard to test what you're saying here. Spent 10 minutes drawing circles on two different Amiga's using four different controllers (a "Boing logo" USB mouse, a generic PS/2 mouse, a trackball, and a clunky-old ball mouse).
Everything was silky smooth on my A2000, with the exception of the classic trackball, which actually felt like it made the most "square-like" circles. On the A500, the ball mouse did seem to make the most "circle-ish" circles, like what you're saying, but in no case were any of these devices some horrible nightmare to use, like what it sounded like you were trying to say. Of course the ball mouse is also 1/5th the DPI so it's easier to make small motions (and less sensitive to shaky hands), but I hated how slow it felt otherwise (and also when the buttons stuck... old clunker, haha).
In hindsight, my testing was flawed because I didn't compare a direct USB connection to USB-through-Cocolino (I could have done this, my A2000 has a RapidRoad). I also should've tried a different mousepad, those Amiga.org logo pads are a bit slippery, and probably all the colors and patterns aren't the best things to use with an optical mouse.
In any case, I think I could count on one hand (with four fingers left over) the number of times I've tried to draw circles with a mouse. That's what drawing tablets are for.
Maybe if I'm really bored tomorrow I'll try with a "less colorful" mouse pad, and with a straight USB connection.
TL;DR. I don't want to deal with a clunky old slow ball mouse, so even with their imperfections I'll continue to use "modern" mice and Cocolino's on my Miggy's. To each their own. Cheers, now enjoy a 10 minute video of me drawing circles!
https://youtu.be/w0wHegf7XLY