What is Zero Beat?
The pitch field has a gap in it where no sound is produced. To find it turn the pitch knob all the way counter clockwise and stand with your pitch had at your shoulder. This should produce a high note. Turn the volume knob clockwise, you should hear the pitch lower and then finally hit a space of silence: that is Zero Beat. The field actually extends behind you as well and leaning back may sound the lowest note again.
*Sadly, we had to bring back ads too. Hopefully more targeted.