This instrument has been designed in the Radiometric Laboratory of the Bureau of Mineral Resources, t o meet the needs of those uranium prospectors who wish to build Geiger counters. The circuit has been designed so that it can be adjusted with a minimum of test equipment. Indication of the count rate is provided by a ratemeter with three ranges; 0-200, 0-1,000 and 0-10,000 counts per minute. Earphones also provide an audible indication of the count rate. The following rate describes the operation of the circuit and the procedure to be adopted to adjust the voltage at various points in the circuit for correct operation. A schematic circuit diagram is also provided and several points concerned with the mechanical design of the instrument are mentioned.