The calibration of pulse oximeters for use on human subjects is regulated by ISO 80601-2-61. This standards document defines minimal requirements for devices, provides classification methods for systems, instructions how to measure accuracy of SpO2 and HR, and lists possible fault conditions. The standards document also provides informative recommendations on how to measure accuracy (Annex CC), standards for calibration (Annex DD), and guidelines for evaluating and documenting SpO2 accuracy in human subjects.