This Technical Report provides information for the understanding and the application of numerical compensation of geometric errors for numerically controlled machine tools including: — terminology associated with numerical compensation; — representation of error functions output from different measuring methods; — identification and classification of compensation methods as currently applied by different CNCs; — information for the understanding and application of different numerical compensations. This Technical Report does not provide a detailed description of geometric errors measurement techniques that are specified in ISO 230 (all parts) and in machine tool specific performance evaluation standards and it is not meant to provide comprehensive theoretical and practical background on the existing technologies. This Technical Report focuses on geometric errors of machine tools operating under no-load or quasi-static conditions. Errors resulting from the application of dynamic forces as well as other errors that might affect the finished part quality (e.g. tool wear) are not considered in this Technical Report. Deformations due to changing static load by moving axes are considered in 7.4.2.