The similarity groups of the pressure differential-current characteristics of solenoid valves are measured in advance, and the measurement results are used to select the solenoid valves to be used for first to fourth pressure increase control valves. This invention is also directed to methods for making the compounds of the instant invention. Each component includes a wall and at least one leg extending from the wall, the leg or legs defining a sliding space. The second differential comparator circuit receives the positive and negative differential clock signal, and generates a second output signal. The cover members are removably attachable to the base members to facilitate mounting of the base members to the exterior wall structure and the attachment of one or more cables to the base member prior to attaching the cover members to the respective base members. In O3 based piezoelectric materials, the surface microstructures of sintered bodies are constituted of microscopic grains having grain diameters of less than 5 \u03bcm, intermediate grains having grain diameters of 5 \u03bcm or more and less than 15 \u03bcm, and coarse grains having grain diameters of 15 \u03bcm or more and 100 \u03bcm or less.