The present invention relates to the field of measurement technology, and provides a ruler which can solve the problem that the existing ruler has few kinds of scales and monotonous display content. In one embodiment, the process comprises an accelerator composition at the pre-cure stage comprised of variable combinations of a dithiocarbamate, a thiazole, a guanidine, a thiuram, or a sulfenamide. The terminal connection patterns at the same position of each circuit board are sandwiched by each of clips of a common terminal member, each of the circuit boards is laminated and fixed, and the converter circuits of each of the circuit boards are connected in parallel. The boxes have sides which define an inner chamber, a heat system, bedding for the female hogs to nest, and insulation covering an open top during cold environment conditions.