Each "Game" has rules made by the person that started it so each has little different like Ricochet's 13mm Funshoot. He wanted a 50 yard 1/2 game but do not want to copy Sawdust's 25 yard 1/4 Inch Club. I suggested to him the 13 mm is .511" and actually closer to one MOA than .500" is. He also liked to save ammo so he made his 4 shot groups. I normally shoot 5 shot groups anyway and that is okay but it has to be at least 4 shot groups. So you see each one is a little different.
The only extra equipment you need is a caliper. I like the digital ones that are 4" instead of 6 inch like most. The 4" are handier for most gun type stuff. I have two 6" Dial calipers left over from my profession in Q.C, and as an engine builder for racing karts and VW Bug engines. I keep one in my range stuff and one is sitting right in front of me as I type this.
The 4" digitals are only about $15 from Harbor Freight and come with the traceability documents that prove they are accurate. I have had mine for 9 years so they have been better for me than dial calipers that are easy to mess up if you get clumsy like me.