This part of ISO10791 specifies, with reference to ISO230-3, tests for the evaluation of thermal distortions ofthe machine structure and positioning system, up to 2 000 mm in length, of machining centres. It gives three testmethods:- environmental temperature variation error; - thermal distortion caused by a rotating spindle;- thermal distortion caused by moving linear axes.There is no intention of assigning any numerical tolerances associated with the tests specified.