I called the tuner who did mine. He said the BHP reading was at the wheel. He did state that it shouldn't be taken too literally as it can differ somewhat on different machines or even on the same machine with a different mechanic and conditions, how it's strapped to the machine etc. He refers to it to see what improvements he is making to the map rather than absolute figures at the end. It's an indication rather than a undisputable figure. As long as the figures are getting better with each tweak to the map then it's going in the right direction.