Horizontal boring and milling machines are one of the most used machines for machining of the shape-complicated and precise workpieces with weight about several tens of tons. Nowadays these machines are frequently used in energy industry where the high demands on the machine accuracy occur. The position accuracy of the tool placed at the end of the headstock is particularly the weakest point of these machines. The position error is caused by gravitation on the horizontal machines conception. Thus this paper introduces the main methods for compensation of this position error.