Nope they arent that accurate, you can get them close that way but they can still drift a fair bit, the better way to do it is pitch percentage ie 0.8 pitch change is 1 bpm for anything around 128 bpm, this is how i did it before i got better at doing it by ear, this way you need to know the tracks bpms beforehand. I still make playlists with the bpm so i can mix quicker in clubs.