Motion capture systems are a must-have part of a modern research laboratory. The system has a wide area of applications such as movie, sport, medicine or experiments validations. The system provides accurate pose and orientation data and allows tracking several objects at the same time. The calibration process is a crucial part of the system, which determines the further accuracy of tracking. This paper presents research struggling with this problem and describes a new approach to the calibration process for the OptiTrack system, using the dedicated application programming interface and its features. The document discusses the general concept, shows the benefits of using it and confirms its usefulness. The working tool is also presented.