Functioning of Equipment 2.4.1 AN/PDR-39 The AN/PDR-39 continued to be an excellent portable, rugged field monitoring instrument that. required little maintenance. There was no moisture or ''sweat" problem, and in general the accuracy was good with little or no drift with age or use. The range resistors were checked with a vibrating reed electrometer bridge circuit. Defective high range resistors were replaced at the beginning of the operation and checked periodically thereafter. The instruments, modified to re- cord up to 500 r/hr, were used considerably for aerial surveys and responded excellently. 2.4.2 AN/PDR-27H The AN/PDR-27H, a beta-gamma survey meter, was a good low range personnel monitoring instrument that had rugged qualities and good stability. 2.4,3 AN/PDR-18 The AN/PDR-18, a gammascintillation survey meter, was used occasionally, and proved to be rugged. It operated with six easy to ob- _ tain flashlight-type batteries, 2.4.4 CDV-700 The CDV-700 beta-gamma survey meter did not perform satis- factorily in this high moisture climate, for the following reasons: a. Frequent power supply failures due to dead batteries, fragile terminal connections, etc,