![Metronome detail [enlarge]](http://farm3.static.flickr.com/2597/3964178034_96a457b363_o.jpg)
Tick tock, tick tock...monotonously goes the pendulum in the metronome. BPM or beats per minute, a unit not only measuring tempo in music but also something so vital as our own heart rate.
..."now, I say, there came to my ears a low, dull, quick sound, such as a watch makes when enveloped in cotton. I knew that sound well too. It was the beating of the old man's heart. It increased my fury as the beating of a drum stimulates the soldier into courage."
..."I swung the chair upon which I had been sitting, and grated it upon the boards, but the noise arose over all and continually increased. It grew louder -- louder -- louder!"
The Tell-Tale Heart - Edgar Allan Poe
