The paper presents the main results of investigations carried out by the author on variation of teeth and base surface accuracy (matching bore and rim faces) of spur gears in the main operations of their machining. The results of the influence of the base surface accuracy and cutting conditions on the teeth accuracy in gear-milling by a worm hob and gear-shaping, as well as the methods of choosing gear-machining manufacturing route and the requirements of their quality in the intermediate operations of their machining providing the necessary quality of completed gears, are described. Information about CTB. 1251-2001 ( State Standard of the Republic of Belarus) that has necessary techniques and recommendations to solve this problem is also given.