2 different dynos,2 very different numbers.why?

I have seen guys here who have bought an engine with a dyno sheet from a few of the big US engine shops, only to see 150 HP less on the dyno here. I guess that 150 hp got left at customs. lol

My local engine builder/ dyno shop is pretty accurate. His engines run what the dyno said it should at the track. MPH+Weight = REAL HP.

Mph+weight= real hp??

I’m not the best with math but I don’t think that’s accurate.