On a serious note, RR are best for showing gains, not actual BHP. So if a company does some work for you, get them to show you graphs before and after, like Paul at RS Tuning does.
This will show you the gains achieved on the same day, same fuel, same rollers, giving you an idea of what the mods have achieved.
The only real way to find BHP is to do the g/s (air) x1.25 sum. For example, my S3 runs 179g/s which means 223 bhp (quoted as 225 from the manufacturer).