| 摘要 |
PROBLEM TO BE SOLVED: To provide a new ruler technique for blackboards in which no deviation is caused to a line drawn with chalk onto a blackboard surface, the blackboard surface is not soiled with chalk powder, a circle without any deviation at a drawing line end can be easily drawn, and moreover a ruler can be smoothly removed from the blackboard surface after the line is drawn.SOLUTION: A triangular ruler body 1 in a right triangle flat plate shape is prepared which has a planar joint surface part 10 of an outer periphery of three sides able to stably join to the blackboard surface 6, and a drawing line edge 11 of three sides able to guide the line drawn with the chalk 5. A pair of collapsible pieces 23 are arranged at a central suitable point surrounded by the joint surface part 10, and are coupled via a hinge mechanism 24 to a suitable point of a ruler outer wall surface side which is the opposite side to the joint surface part 10. The pair of collapsible pieces 23 is equipped with a soft attraction part 20. Moreover, an attracting mechanism 2 deformable to either one and alternately with each other of a sitting attraction posture and a collapsing detachment posture is built in the ruler for the blackboard. |
