OK what you need here is something called a Sirometer, which is a tool for measuring RPM based on vibration / resonance. Here is a link: http://www.treysit.com

OK what you need here is something called a Sirometer, which is a tool for measuring RPM based on vibration / resonance. Here is a link: http://www.treysit.com/16.html http://www.treysit.com/16.html