GEMS PET Systems AB develops and manufactures medical cyclotrons. Cyclotrons are used for producing radioactive isotopes for medical substances. A cyclotron consists mainly of a large electromagnet and a target system. The quality of the magnetic field, created by the electromagnet, is very important for the function of the cyclotron. The aim of this project is to develop the mechanical design of an automated mapping device that in an easy and precise way can guarantee the quality of the magnet and its field before the magnet is mounted in the cyclotron and taken into use. The mapping device has to give high precision mappings, fit cyclotron magnets of two different sizes and should be assembled to map a perfect plane with as few after adjustments as possible. The project in its whole has been based on the method of systematic problem treatment combined with Pahl and Beitz problem solving methods. Nine different concepts were generated and thorough examinations and discussions led to a final concept that was modeled, drafted, manufactured and assembled as a fully functional prototype. Strain, stress and finite element calculations have been made to ensure the functionality of the device. The mapping device consists of a support and adjustment assembly, a mapping assembly and motion creating units. Most parts of the mapping device are made out of aluminum alloys and a few smaller details and the fasteners are made of nonmagnetic stainless steel. The support and adjustment assembly are positioned on top of the magnet and hanging over its sides like a yoke. The central elements in the mapping device are three linear units with motor driven moving sleds. The two vertical linear units are adjustably fastened to the yoke and the horizontal linear unit is fixed to the sled of one of the vertical units. The mappings are done by three Hall probes attached to a high precision aluminum rail. When running the mapping device the sleds move in 5 mm steps. Everything attached, directly or indirectly, to the sleds, such as rail and measuring probes follow these movements. Each stop becomes a mapping point where the probes measure the magnetic field. Together the points form a fine grid of data readings. Many of the flaws with the old measuring device are eliminated by this new one. The new mapping device fits both magnet sizes, and it is easy to position and adjust. The support structure makes the device stable and durable. The probes are well positioned and protected in a case that is attached to the rail. The rail runs smoothly on wheels attached to the vertical sleds and has a very high straightness and low vertical displacement, which makes the mappings very reliable.