CDJ-800 displays fast and accurate bpm.
But because it measures in full beats-per-minute it must round the value. In otheer words : 121.6 and 122.4 both will be displayed as 122 BPM. The last part of pitching the tracks is always the art that remains DJing
It is NOT accurate with some R'n'B, hip-hop and drum'n bass tracks. It needs some form of 4-quart-measure to calculate it's BPM. This doesn't have to be a bassline, also a lot rhythmatical or instrumental lines are recognized, but when things get to tricky you're on your own again :D