I used to pilot small 4 seat aircraft and I would look up the specs on certain aircraft. Take off over 50' obstacle, landing distance, the best rate of climb, cruise speed, etc. While air temperature, altitude, and relative humidity play an important part, I could never duplicate the specs. I mentioned it to my old flight instructor, and he said those measurements were done in "factory air" (smile). After numerous tries, they take the best results which seldom occurs in the real world.