Racing flow benches

When I finished building my flowbench and loaded the info on my laptop you go into calibration and (choose your plate size) I started at 300cfm. after it’s in place start the flowbench. If by chance it was 298-301 you lucked out. If not you go to the configure screen and raise or lower your number to dial it in. T

I would to have a bench. What does it take to build one?