PURPOSE:To enable to decide simply whether filter countermeasure is necessary or not by short-circuit capacity and inverter capacity of a power distributing system by superposing the first and second circular sheets in which specified scale is written and adjusting their relative position. CONSTITUTION:The first and second circular sheets 1,2 are superposed and their centers are pivoted freely rotatably. Scales that indicate inverter capacity and short-circuit capacity of the distributing system are written in the first circular sheet to have predetermined interrelation. A pointer 21 to point the scale that indicates the inverter capacity written in the first circular sheet 1 and information for deciding the presence or absence of higher harmonic impediment based on the pointer 21 are written in the second circular sheet 2.
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