I have used the Shinwa american pattern squares for at least twelve years and I am completely happy with them. Since I layout with an awl, no pencil marks, I have placed friction tape down the center on the back side which aids greatly with suppressing movement of the square when striking lines. I also use the tenths and twelths from time to time.
The twelths are a key into older methods of layout in buildings with odd fractional roof slopes. The carpenter knowing only the overall rise and run can layout the roof with the twelth scale without calculation of slope, run per foot or angular degree. If for example, run = 14-7 and rise = 9-2 then hold 14 7/12 by 9 2/12 and step twelve times for rafter length.
