OTC 3660 Phototach Non-Contact Tachometer Four styles of contact adapter tips clip easily to the top of the Phototach and the Infrared technology makes the Phototach accurate convenient and easy to use Infrared beam is not affected by ambient light and the non-contact design results in zero torque loss for true precision Equipped with a laser pointer for accurate targeting and reflective tape placed on a revolving object can be measured at distances from 2 inch to 20 inch Wide measuring range and high resolution 2.5 to 99999 rpm with a large 5-digit display Autoranging min/max memory storage and low-battery indicator