Nakaoki Ōita

Naka-oki, 中置, middle-place, arrangement with fu-ro, 風炉, wind-hearth, set on an ō-ita, 大板, large-board; 14 x 14 sun kane-jaku. The center of the ōita is placed in the center of the han-jō, 半畳, half-tatami, equidistant from the four edges of the tatami. Placed in front of the ōita is the ya-hazu ita, 矢筈板, arrow-nock-board; length 14 x 9 sun kane-jaku.

Perhaps the Nakaoki arrangement with ōita is the origin of the size of the yahazuita. The yahazu-ita is used to display a hana-ire, 花入, flower-receptacle, in the tokonoma, and most often placed in the middle of the tokonoma, rather like a Buddhist altar. There are slight variations of both boards, as the specific measurements may not have been followed. The yahazuita is the most formal of the four usu-ita, 薄板, thin-boards, used to display flowers in the tokonoma. The width of the ōita and the length of the yahazuita are, ideally, 14 sun kane-jaku. The 14 sun kane-jaku measurement is the width of tatami allotted to the host, tei-shu, 亭主, house-master.  

The number 9 is close to the 8.8 sun kane-jaku measurement between the ōita and the front edge of the tatami. The measurement of 8.8 sun kane-jaku is the standard distance between the shiki-ita, 敷板, spread-board, of the furo and the knee line of the teishu, or the front edge of the han-jō, 半畳, half-tatami, pictured above. This measurement is usually established in Kyō-tatami by drawing a line from 16 tatami me, 目, interval, from the heri binding of the adjoining ki-nin tatami, 貴人畳, noble-person mat. The number 8.8 is symbolic of Infinity in Space.  

For further study, see also: October and Nakaoki, Tea in October, and Tokonoma and Imae