BPM values are slightly below the actual values

[juandmi]

Thanks Adam for this great repository and for sharing it with everyone. I compiled it and found that the BPM values are most of the time a bit lower (1 - 4) than the actual values. You can find the details of my approach here. https://github.com/juandmi/BTrack/blob/master/BPMCalc/README.md It would be great if you could check and tell me if I'm doing something wrong or if this discrepancy is normal.