The AT-30-B is a rugged, transistorized alternator or magnetic pick up signal analog tachometer with solid-state circuitry for indication of engine RPM. It is equipped with a bracket for mounting into a standard 3-3/8" (86 mm) dash mounting hole, and has a bright 304 stainless steel bezel. This model is powered by a 11-28 VDC battery and is reverse polarity protected. A full 270° sweep of the pointer gives an accurate indication on a large easy-to-read scale, ranging from 0 to 3000 rpm. The dial can be illuminated for night reading using through dial lighting.  poles on therotor. This model replaces ATA-30-12 (20700175) and ATA-30-24 (20700198) and ATA-40 models.