A method and apparatus for generating a clock that can be switched in phase within a reduced interval of dead time are disclosed. It is determined whether or not a device itself satisfies a specific condition, and, depending on a result thereof, an instruction to set or release the specific condition is issued to all client devices sharing the data. The apparatus including a railway upon which a train travels. The shimming plate is placed between a tool bottom part, alternatively a tool top part, and the blank holder ring, alternatively the draw ring. The use of the apparatus that measures the patient’s peripheral blood perfusion allows for an efficient and convenient means of cardiac gating while avoiding occlusion of diagnostically important anatomy.