Defines a procedure for the non-destructive measurement of coating thicknesses using beta backscatter gauges. Relates to both metallic and non-metallic coatings on both metallic and non-metallic substrates. To use this method, the atomic numbers or equivalent atomic numbers of the coating and the substrate must differ by an appropriate amount. Includes references to definitions, principle, instrumentation, factors relating to accuracy, calibration of instruments, measuring procedure, measuring accuracy and precision, test report, isotopes used with beta backscatter gauges, atomic numbers of some commonly used coatings and substrates and saturation thickness.