This report describes facilities primarily designed for uranium exploration instruments, but also discusses the use of these facilities for the calibration of radiation protection instruments. Contents: 1. Introduction; 2. Basic radiation geophysics; 3. Instruments used in radiation surveys; 4. Quantities and units; 5. Relations between instrument readings and the corresponding field assay values; 6. Calibration systems; 7. Design considerations for calibration pads; 8. Construction of calibration pads; 9. Calibration.