The CD V-700 is a Geiger counter employing a probe equipped with a Geiger–Müller tube manufactured by several companies under contract to US federal civil defense agencies in the 1950s and 1960s. This unit is quite sensitive and can be used to measure low levels of gamma radiation and detect beta radiation.  In cases of high-radiation fields, the Geiger tube can saturate, causing the meter to read a very low level of radiation (close to 0 R/h) hence the necessity of the companion ion-chamber survey meters.