A method of constructing an exhaust heat recovery boiler. The third lens unit consists of a first lens subunit of positive optical power, an aperture stop, and a second lens subunit having one or more negative lens elements and one or more positive lens elements, in order from the object to the image sides. Based on this data, a three dimensional digital data file is then created substantially corresponding to the dental prosthesis to be manufactured. Also, the bus wires are easily extended from the armature, and an amount of work required to connect the bus wires and the terminals is reduced. To remove sleep delay, a slot next to the signal reception slot becomes a signal transmission slot. , a QPSK constellation, a 16-QAM constellation, etc.