A depth gauge for measuring the depth of blind holes in bones andor nails inserted into bones is provided. A problem determination device is provided in which the problem determination device sends an electrical signal to the electric motor such that the electric motor rotates in a direction opposite that of the direction of rotation to generate a brake force. The dye has a fluorescein structure. Articles to be coated are suspended within the coating chamber, and transported with a support apparatus relative to the two molten pools so as to deposit a coating with a controlled composition that is a mixture of the first and second materials. Thus, the problems of the prior art could have been solved.