The detector is a 22.9 cm (9 in.), moderated ³He tube with a gamma background rejection up to 100 mSv/h (10 R/hr). The ratemeter is a four-decade analog meter, designed with an aluminum cast instrument housing incorporating a separate battery compartment, and accompanying metal handle. This design delivers industrial robustness and quality, promoting long-lasting protection and instrument life.

The front-panel controls include a rotary switch for selecting the four-decade range, instrument shut-off, and battery test, an audio on/off switch, a fast/slow response switch, a count reset, and high-voltage test push-button. The Model 12-4 is a complete turn-key system and includes two “D” cell batteries.