12,961. Erwin, C. June 9, A.D. 1902, [date applied for under Patents Act, A.D. 1901]. Arithmetic, teaching.-Relates to a device for teaching numbers. A frame has a back a, Fig. 4, of wood or other material, and along the lower edge of its front face are fixed strips c, b which form a pocket d. End strips e are also secured to the back, and to them is attached a guide-board f, Fig. 1, which may be used as a blackboard. Secured to the back are equidistant strips g bearing consecutive numbers, the lower ends resting in the pocket, the upper ends fitting between the board f and the back. The spaces between these strips receive movable strips h, which are numbered on both sides, the number on one side of a particular strip being one higher than that on the corresponding side of the preceding strip. Notches k facilitate insertion or withdrawal.