We used to have problems with folk claiming that a PTO power was way down on the stated engine power.
They ignored transmission losses.
On one particular model of tractor, at our insistence, one engine was PTO tested against a large enough number of transmissions to be statistically significant . Losses varied between 5 bhp and 32 bhp!
Another major customer complained of low power outputs.
Their tests were carried out as stall down tests, at dealerships all across Europe, using unknown fuels, and under unknown ambient conditions..
When I asked what was the range of transmission losses, no one seemed to have considered them. Subsequent work showed the transmission losses to have a wide spread!
To test generators for welding sets, we had to buy a special load bank which was quite different from those used for conventional gensets. Dissipating 40Kw at 20 volts, DC or AC, called for a quite different set up from 40 Kw at 450 volts three phase.
Howard