An oxide phosphor that is highly durable and produces visible light when excited by exposure to near-ultraviolet excitation light, comprising an oxide having the composition represented by the formula x. The vacuum pump is controlled by a processor and is automatically activated when the vacuum is below a pre-selected parameter or a parameter selected on the fly by the surgeon. The method further comprises obtaining location data for a first object, wherein the location data is based at least in part on a beacon signal associated with the first object, and rendering a graphical representation of the first object on the display device. An evaluation unit includes a comparison unit to compare a respective effectiveness of the first hash function and the second hash function, and an exchanging unit responsive to the comparison unit adapted to replace the first hash function by the second hash function.