tundraotto
Addicted to ArboristSite
Doug, I believe that they are truly inductive. I say this since the "sensoring end" is metal plated on the tech tach - ie. electromagnetic pickup. They work accurately on a multicylinder environment too, which I would imagine would preclude any type of audio pickup. Just point to the plug wire and you get the reading - if you offset too much from the pickup end you will lose your reading.