Contamination meters are instruments for surface contamination measurement. Generally, surface contamination means that radioactive material has been deposited on surfaces (such as walls, floors). It may be loosely deposited, much like ordinary dust, or it may be quite firmly fixed by chemical reaction. This distinction is important, and we classify surface contamination on the basis of how easily it can be removed. In nuclear facilities, contamination monitors are installed usually at the exit from the controlled areas. These monitors may utilize proportional counters with a large area, thin window detector similar to Hand & Shoe Monitors. When instruments are operated in the proportional region, the voltage must be kept constant. If a voltage remains constant the gas amplification factor also does not change. Proportional counter detection instruments are very sensitive to low levels of radiation. By proper functional arrangements, modifications, and biasing, the proportional counter can be used to detect alpha, beta, gamma, or neutron radiation in mixed radiation fields. The electronics sorts the alpha, the beta-gamma pulses and displays both in a bar-type display.