Biddle Instruments 359982 DHR905 8603.909 Digital Tachometer

The Biddle 359982 Digital Tachometer is a compact, portable hand instrument that measures rotational speed by directing an infrared beam at a taped target on the rotating surface and showing the RPM on a four‑digit LCD display. The sensing head combines a phototransistor “eye” with an infrared LED and a pulsing target LED for a clear, photoelectric reading, with a dedicated recharger jack and a battery pack holder for on‑site use. It is powered by six alkaline AA cells (supplied) and includes a mounting hole for tripod use, a straightforward operating button, and a transparent display window for quick readings, while noting that the unit is not sealed and should not be used in explosive atmospheres or in high humidity environments. Displayed RPM ranges cover low to high speeds, from 100.0–999.9 up to higher bands reached through scale multipliers, enabling readings for a wide variety of motors and spindles without swapping instruments; the device is designed for on‑site measurements with a compact, lightweight form factor that supports easy handling and quick checks on rotating equipment.