The diploma thesis deals with the analysis of a pneumatic measuring system for spools in hydraulic valves. The spools must be ground to a tolerance of a few micro meters, and in order to improve the quality of the spools and the production process, an appropriate measuring system must be provided to control the production of the spools. For the analysis of the measuring system, we chose one of the Six Sigma methods to calculate the repeatability and reproducibility of the chosen measuring system. The thesis presents three analyses. The first one is the analysis of a mechanical measuring system operating on the principle of two-point measuring method, the other two analyses comprise a pneumatic measuring system which is based on measuring the average diameter of a spool.