The DP-66 were developed alongside the Russian Military DP-5 series of Geiger counters under the Warsaw Pact for Poland, a satellite state of Soviet Russia. These survey meters were built for local and state civil defense in case of disasters and/or nuclear holocaust. The DP-66 and are both able to measure beta and gamma radiation from 0.05 mR/hr to 200 R/hr in 6 ranges and are both able to charge the DKP-50 series of optical pen dosimeters (measuring up to a 50 Roentgen dose). They also have the ability to zero the scale when going up to a higher range which is a reoccurring problem in the design of the American CDV-700. Another unique feature that is different from the Russian DP-5 is that they have 3 GM tubes that are turned on based on the range selected, the Russian DP-5 only has two which are running all the time. Both the DP-66 and DP-66M come with an operational 10 μCi Sr-90/Y-90 check source, but it has since been removed per NRC regulations. Another notable feature is that they come with an extension wand to prevent contamination of your skin when measuring possibly contaminated/radioactive materials. They are powered by 2 D cells which is different than the custom DP-5 batteries that are made only for the instrument and are so hard to find you have to dangerously modify existing batteries or use a DIY AA battery adapter to make it work. The DP-66 is able to measure in decays/min per every square centimeter which is done by reading the top scale of the meter and dividing the readings by the average measured background gamma radiation. This unique contamination scale is a defining feature of the DP-66. The DP-66 is also notable to have more functionality with a better probe design and a unique Beta times 10 position in which the maximum in decays/min*cm2 range of 1 million being the max to increase to about 10 million decays/min*cm2. The DP-66 saw service until the early 1970’s when it’s circuit design was improved and the DP-66M was born. The DP-66M was the second iteration of the DP-66 which featured a spring loaded probe to “pop” the beta shield if measuring beta radiation. The contamination scale and the beta times 10 function were removed and replaced by newer electrical components. The audio was improved in response to complaints of the audio getting higher in pitch for each higher range. The only downside to these units is that they are somewhat temper-mental and that some units are sensitive to agitation of the cord connecting the unit to the probe. Bulky as they are, they are not as bulky to carry around as a CDV-700 since they can be carried around your neck and the probe can be safely stored while not in use. Overall an excellent very sensitive unit with a history that unparallel any other of its kind. The set we include: – The instrument together with case, – Wooden suitcase transport – Miniature ear headphones - Power supply (r20 battery) Packaged in the original case dimensions: 47 x 16 x 25 cm Weight: 7.5 kg Registered shipping with Track & Trace.