This part of IEC 63203 defines the terms, definitions, symbols, configurations, and test methods to be used to specify the standard measurement conditions and methods for determining the contact surface temperature of wrist worn wearable electronic devices for preventing low temperature skin burn. This document applies to electronic devices that are intended to be worn directly on human wrist and may be worn continuously during use. This document specifies conditions under which contact surface temperature is measured to ensure that the contact surface temperature of the device is below temperature which can cause human skin burn, taking into consideration the device use conditions and the effect of human skin temperature. The conditions of the test do not consider perfusion and results should be considered as conservative. The temperature increase is induced by the thermal energy of wearable electronic devices during operation. This document does not specify temperature limits. Temperature limits are specified in other documents, such as IEC 62368-1 as described in Annex A. Temperature limits from IEC 62368-1 are based on an ambient of 25 ºC. This part of IEC 63203 is the general procedure for the test method applicable to various wrist worn wearable electronic devices for use by ordinary persons which in the context of this document is a healthy human adult.