PURPOSE: To ensure a quick and accurate operation before start of the calculation by securing the revolution for the upper frame of the 5-bead side of abacus between the edge parts of the side frame and from the upper side to the rear side centering on the beam side.

CONSTITUTION: For calculation via the abacus, both 1-bead 6 and 5-bead 8 are separated from beam 4. In that case, the 5-bead side is lifted up slightly. As 5- bead digit 7 features a free end in approximation to the side of beam 4, upper frame 3 turns round with its empty weight with the axle support part 10 of arm 9 used as the fulcrum. And pin 11 reaches the lower end of groove 12 to stop there. Arm 9 has only the revolution since is adhered to frame 3, and frame 3 is tilted with the face attached with digit 7 turned up. And 5-bead 8 moves toward frame 3 by its empty weight; while 1-bead 6 moves toward lower frame 2. Accordingly, if the abacus is put on the desk under these conditions, both the 1-bead and 5-bead are set regularly at the prescribed positions before start of the calculation. In such way, a quick and accurate operation can be secured for start of the abacus calculation without operating the beads by fingers.