OTC Tools OTC 3665 Phototach Contact / Non-Contact Tachometer. No. 3665 phototach can be used as a contact as well as a non-contact tachometer. Four styles of contact adapter tips clip easily to the top of the phototach. Infrared technology makes the phototach accurate, convenient, and easy to use. Infrared beam not affected by ambient light. Non-contact design results in (zero) torque loss for true precision. Phototach is equipped with a laser pointer for accurate targeting. Reflective tape placed on a revolving object can be measured at distances from 2" to 20". Wide measuring range and high resolution, 2.5 to 99,999 rpm with a large 5-digit display, autoranging, min/max memory storage, and low-battery indicator.