Measured using 4-wire Kelvin method. Difference from a reference length of wire (voltage drop method). Minimum pull-out force (N) = function of wire cross-section (mm²) and strand class.
For Class 5/6 (fine strands), force may be reduced by ~20% if specified. iec 60352-2 pdf
Latest active version (as of this report): IEC 60352-2:2020 RLV (Redline version) – supersedes earlier editions (2006, 1990). Measured using 4-wire Kelvin method