2 different dynos,2 very different numbers.why?

Personally I think dyno's are for people who either don't know a damn thing or people know way too much. I've got hundreds of Dyno sheets on my motor all of them are about a foot long and 3 in wide and not one of them tells a lie.
My "Dyno" is a 73 Duster! I would be more than glad to LOL put anybody's motor on my Dino, Run it in for 20 minutes and then give it a time slip that will be 100% guaranteed accurate horsepower reading.
Edit: I'll be having a half-price sale for the rest of the year! LOL