| 摘要 |
An educational tool including a rigid frame supporting a pair of parallel rods. A number of beads of equal width are slidably positioned on one of the rods. A reckoning slide is slidably and rotatably positioned on the other of the rods for counting the beads. The reckoning slide has a front side and a rear side, either of which may be selectively brought into view by rotating the reckoning slide. The front side has printed indicia in the form of a first whole number sequence increasing from left-to-right and the rear side has printed indicia in the form of a second whole number sequence increasing from right-to-left.
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