IEC 60904-10:2020 describes the procedures used to measure the dependence of any electrical parameter (Y) of a photovoltaic (PV) device with respect to a test parameter (X) and to determine the degree at which this dependence is close to an ideal linear (straight-line) function. It also gives guidance on how to consider deviations from the ideal linear dependence and in general on how to deal with non-linearities of PV device electrical parameters. This third edition cancels and replaces the second edition published in 2009. This edition includes the following significant technical changes with respect to the previous edition: a. Modification of title. b. Inclusion of an Introduction explanatory of the changes and the reasoning behind them. c. Inclusion of a new Clause Terms and Definitions (Clause 3), with distinction between generic linear dependence and linear dependence of short-circuit current versus irradiance (linearity). d. Explicit definition of equivalent sample (Clause 4). e. Technical revision of the apparatus (Clause 5), of the measurement procedures (Clause 6 to Clause 8) and of the data analysis (Clause 9), with separation of the data analysis for a generic linear dependence from the data analysis specific to linearity (i.e. short-circuit current dependence on irradiance) assessment. Additionally, inclusion of impact of spectral effects on both linearity and linear dependence assessment. f. Introduction of specific data analysis for two-lamp method, making it fully quantitative. Addition of extended version called N-lamp method. g. Modification of the linearity assessment criterion with inclusion of a formula that can be used to correct the irradiance reading of a PV reference device for non-linearity of its short-circuit current versus irradiance. A linearity factor is specifically newly defined for this purpose. h. Revision of the requirements for the report (Clause 10) in order to improve clearness about what information is always necessary and what is dependent on the procedure actually followed to measure the linear dependence, including the type of dependence measured (generic or linearity).