This part of ISO 230 defines three tests for the determination of thermal effects on machine tools: ? an environmental temperature variation error (ETVE) test; ? a test for thermal distortion caused by rotating spindles; ? a test for thermal distortion caused by moving linear axes. The test for thermal distortion caused by moving linear axes (see Clause 7) is applicable to numerically controlled (NC) machines only and is designed to quantify the effects of thermal expansion and contraction as well as the rotational deformation of structure. For practical reasons, it is applicable to machines with linear axes up to 2 000 mm in length. If used for machines with axes longer than 2 000 mm, it will be necessary to choose a representative length of 2 000 mm in the normal range of each axis for the tests. The tests correspond to drift tests according to ISO/TR 16015 and define the evaluation and the detailed procedure for machine tools. NOTE It is not foreseen that numerical tolerances will be determined for the tests specified in this part of ISO 230.