In the latter half of the eighth century, the Japanese began using incense to mark time by placing a stick of it horizontally in a wooden box with holes marked at specific intervals. You could tell how much time had passed by noting which hole the smoke was coming from. An incense stick could be made with a number of different scent blends, so that simply sniffing the air would indicate the time. (This scented method of keeping time was so efficient that until 1924, geishas were still paid by the number of incense sticks lit during their time with a client.) (From The Elements of a Home: Curious Histories Behind Everyday Household Objects, by Amy Azzarito)
Sylvia Shults, author 