During rotor balancing, the balance quality is assessed. During this process, errors may occur which can originate from a number of sources. It is therefore necessary to take into account the detected errors. Thus this standard gives examples of typical errors that can occur and provides recommended procedures for their evaluation. Furthermore generalized methods for assessment of residual unbalance are described, taking into consideration existing errors. The standard covers the following: a) identifying errors in the unbalance measuring process of a rotor; b) assessing the identified errors; c) taking the errors into account. This part of ISO 21940 specifies balance acceptance criteria, in terms of residual unbalance, for both directly after balancing and for a subsequent check of the balance quality by the user. For the main typical errors, this part of ISO 21940 lists methods for their reduction in an informative annex. The International Standard ISO 21940-14 "Mechanical vibration - Rotor balancing - Part 14: Procedures for assessing balance errors" has been prepared with the German collaboration as a revision of ISO 1940-2:1997 by ISO/TC 108 "Mechanical vibration, shock and condition monitoring", Subcommittee SC 2 "Measurement and evaluation of mechanical vibration and shock as applied to machines, vehicles and structures", the secretariat of which is held by DIN. Regarding the German collaboration the responsible committee is NA 001-03-06-01 (NALS/VDI C 6.1) "Auswuchten und Auswuchtmaschinen" ("Balancing and balancing machines"). This standard differs from DIN ISO 1940-2:1998-02 as follows: a) the number of the standard has been changed; b) the scope has been extended to include rotors with flexible behaviour; c) data used to check the influence coefficient method have been deleted; d) the standard has been editorially revised and adapted to the current terminology.