Measuring device

A measuring device, comprising:

• a spatially-movable probe head;
• an optical position sensing device adapted to determining a spatial position and orientation of the probe head relative to a reference point, the position sensing device including at least three position determination modules, arranged as a transmission unit, including at least one transmission unit marking element, or as a receiving unit, including at least one optoelectronic detector and at least one receiving unit marking element arranged in a defined spatial relationship relative to the optoelectronic detector, at least one position determination module arranged on the probe head, at least one position determination module arranged at the reference point, at least one position determination module arranged as a receiving unit;
• wherein visual contacts exist between at least some of the position determination modules;
• and
• wherein the position determination module arranged on the probe head and the determination module arranged at the reference point are connected by at least one uninterrupted chain of visual contacts.