This part of ISO 13041 specifies, with reference to ISO 230-3, the tests which apply for the evaluation of thermal distortions of the machine structure and positioning system, up to 2 000 mm in length, of numerically controlled (NC) turning machines and turning centres. Hence, this part of ISO 13041 defines three tests which are - the environmental temperature-variation error test, - the test for thermal distortion caused by a rotating spindle, and - the test for thermal distortion caused by moving linear axes. It should be noted that there is no intention of assigning any numerical tolerances associated with the tests described in this part of ISO 13041.