The CD V-715 is a portable monitoring instrument which measures gamma radiation dose rates as high as 500 roentgens per hour. It is designed to be used by radiological Civil Defense personnel in determining radioactive contamination levels that may result from an enemy attack or other nuclear disasters. Instrument accuracy on any of its four ranges is within ± 20% of the true dose rate from Cobalt 60 gamma radiation. This accuracy is maintained throughout a temperature range of -20° F to +125° F, relative humidities to 100% and at altitudes from sea level to 25,000 feet. The detecting element is an hermetically sealed ionization chamber. This chamber is located in the lower front portion of the instrument to make the instrument equally sensitive to radiation from the bottom and front. The ionization chamber plus the instrument case will together total more than 1000 mg/cm2 in effective thickness to make the instrument insensitive to beta rays lower than 2 Mev in energy. The ionization chamber is hermetically sealed to eliminate changes in sensitivity due to changes in air pressure resulting from altitude changes, temperature changes, and moisture effects.