This is a Gates sonic tenison meter. It can be used on all types of drive belts, PowerGrip Timing Belts, PowerGrip HTD Belts,
PowerGrip GT Belts, Poly Chain GT Belts, Polyflex V-Belts, Micro-V Belts and more. E-Bay get around $250.
Mine is in Perfect condition and a complete kit. $50 cash.