Huh. I'd have expected it to be based on the center, but I guess the goal is "it must be entirely within this ring to count" rather than just "I hit this ring".
They use wave detection from each corner - either air/sound or via the target backing - to triangulate and with modern electronics can be quite accurate.
It's nice from an audience point of view to be able to see the results of each shot almost immediately. Kinda like watching snooker championships.
This approach is novel however and has other pros and cons.
Um... No. An american 22 can be very slightly smaller. American-invented calibers are measured to the depth of the grooves in a rifled barrel. The rest of the world measures to the flat parts between the grooves. So no, it is not obvious how wide a bullet is.
And beware the plural. If someone (usually a salty navy person) says that a gun is "50 calibers" he means something completely different than a "50 caliber".
I totally see the programming challenge there, but it's in no substantial way making the journey any easier. Any somewhat working human brain can count this quite quickly and then move on with other things.
Really, I don't get it.