Presented is a method for determining the tolerances in geometric precision of machining centers in working conditions. The method is based on the implementation of coordinate measurements with contact measuring head. The measurements are performed on special prismatic detail – caliber attachable with relatively low grade precision guidance on the machine table. In the publication are presented experimental studies and the results obtained. The conclusion is that the developed method, the mathematical model and caliber are suitable for the determination of some basic elements of geometric precision of machining centers in working conditions. At the same time provides a satisfying user accuracy, cost and performance.