This part of IEC 62496 specifies a method of defining the conditions for measurements of optical characteristics of optical circuit boards. The method comprises the use of code reference look-up tables to identify different critical aspects of the measurement environment. The values extracted from the tables are used to construct a measurement identification code, which, in itself, captures sufficient information about the measurement conditions, so as to ensure consistency of independently measured results within an acceptable margin. Recommended measurement conditions are specified to minimise further variation in independently measured results.