Smith, David Eugene; Mikami, Yoshio (1914). "Chapter III: The Development of the Soroban.". A History of Japanese Mathematics. The Open Court Publishing. pp. 43–44. digital copyArchived 2010-12-03 at the Wayback Machine[ISBN missing]
Smith, David Eugene; Mikami, Yoshio (1914). "Chapter III: The Development of the Soroban.". A History of Japanese Mathematics. The Open Court Publishing. pp. 43–44. digital copyArchived 2010-12-03 at the Wayback Machine[ISBN missing]