As far as happy scales and engine and chassis dyno, if they are NOT calibrated correctly they are not giving you correct information , been there and had that done to me several times
I've seen many engine dyno rooms have test room have positive air pressure inside of them due to the inlet fan for outside air flow more CFM than the exhaust fans did resulting in positive pressure in the dyno cell Talk about phony results due to the positive inside pressure, it is just like adding 1 to 3 Lb. boost to the motors