| 摘要 |
A calculating rule comprises three coaxial cylindrical elements displaceable relative to one another by rotation. The outer cylinder has at least one transparent window and the intermediate cylinder is transparent. Each cylinder carries an index line serving as a reference line or carrying graduations. At least one of the index lines is helicoidal so that one index line intersects the two others at an angle different to 90 DEG . Preferably, rotation of the intermediate cylinder relative to the outer one causes automatic rotation of the inner cylinder, but not vice versa. At least one of the elements can be planar. |
