There are rectangular holes called byojo on several of the bamboo tubes, and their lengths as resonant tubes are determined by the locations of this holes, not by the entire length of the bamboo tubes.
いくつかの竹管には屏上（びょうじょう）と呼ばれる長方形の穴があり、共鳴管としての管長は全長ではなくこの穴で決まる。