The object of the present invention is to provide a main shaft balancing device for a machine tool, in which a gas spring is used in order to have reliable and effective reduction of the load on a vertical displacement means which raises and lowers a main shaft unit. The communication wire protecting tube includes at least two synthetic resin layers, and inserts the communication wire in a loose state. In one embodiment, the activator composition having a siloxane moiety represented by the formulae:. The flowmeter includes a controller in electrical communication with the plurality of transducers which determines the gas flow rate through the channel by measuring transit times of signals transmitted by and received by the transducers. An associated digital compensation filter and an associated calibration circuit are also provided. A final design including the number of engineering options associated with resources in which the final design is for building the selected option in the aircraft is generated using the number of engineering options identified in the aircraft option database for the selected option.