Very true. In the past I had a ford focus svt tuned at a local performance shop after they got done tuning the car they performed a dyno test and showed I had 215 at the wheels. Which I was super happy cause at the time I had not done nothing major to the engine. Later at one my local car shows that we having in the spring came around they had a mobile dyno test machine. I got it up their and they did the run and showed I had lost close to 20 hp. I was not happy by this so later I took it back to the shop and they ran another test and it still came back to 215. I was really surprised by this and the guy told me it comes down to how used the dyno is as well for the calibration being done. So it comes down to how the machine is set up and how often it calibrated.