Figure 2 Analog-Digital Meter
In the 1960's, at the height of the Cold War over half a million Civil Defense CDV-715 ion chamber radiological instruments were manufactured, see figure 3. In its day the CDV-715 could be found in government fallout shelters across the country. Unfortunately, this survey instrument only detects high levels of gamma radiation that would be encountered in a post nuclear attack or incident. So even good working CDV-715 models are not sensitive for most radioactive detection work.