At Zen-sect temples, time consumed until a stick of Senko burns out (about 40 minutes) was called Icchu and it was used as the unit time for Zen meditation.
禅寺では線香が1本燃え尽きるまでの時間（40分）を一炷（いっちゅう）と呼び、坐禅を行う時間の単位とした．