IEC 60904-4:2019 is available as IEC 60904-4:2019 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.

IEC 60904-4:2019 sets the requirements for calibration procedures intended to establish the traceability of photovoltaic (PV) reference devices to SI units as required by IEC 60904-2. This document applies to PV reference devices that are used to measure the irradiance of natural or simulated sunlight for the purpose of quantifying the performance of PV devices. The use of a PV reference device is required in many standards concerning PV (e.g. IEC 60904-1 and IEC 60904-3). This document has been written with single-junction PV reference devices in mind, in particular crystalline silicon, but it is sufficiently general to include other single-junction technologies. This second edition cancels and replaces the first edition published in 2009. This edition includes the following significant technical changes with respect to the previous edition:
modification of standard title;
- inclusion of working reference in traceability chain;
- update of WRR with respect to SI;
- revision of all methods and their uncertainties in annex
- harmonization of symbols and formulae with other IEC standards.