2 different dynos,2 very different numbers.why?

I have to agree with IQ52 it's all math anyway. I had a RZV500R Yamaha, for you that don't know what it is It is a Japanese 500cc 4cyl 2 stroke Moto GP replica that Yamaha made in 85 and 86 only and never got them in the states, but It made 90 HP on the Dyno at 10.000 rpm, another dyno it made 100 HP at 10.000 RPM. long story short the guy that had the 90 HP dyno bad mouthed the other guys shop for having a riged dyno.
It was a very fun bike to ride 320 lbs 90+HP, One of the baddest bikes of It's era.