Instructions: Web browsers aren't great at keeping accurate time. If you want an accurate BPM, then you can hook up an external sampler or drum machine to your computer (via MIDI interface) to keep time. Tell the drum machine to play 16 straight sixteenth notes, and this machine in the browser will update its count every time your external drum machine plays a note. Click the "MIDI" button, and try it out! While MIDI is off, the browser will keep time on its own. Press "C" on your keyboard to clear the tracks.