Olden days calculator

This 'calculator', known as an abacus, was used by my grandfather in the olden days to run his provision shop. In those days, they did not have calculators to help them calculate the prices of the goods and the total cost of his customer's items, using the abacus helped them calculate the cost without pen and paper. The abacus has 2 beads on the upper rod and 5 beads on the lower rod. The amount is counted by moving beads up and down the rod. If the bead is moved towards the beam, the value is counted, if the bead is moved away from the beam, the value is not counted. It can also be easily be resetted by a jerk. The abacus could also be used by the blind by adding a soft fabric or rubber so that they don't move inadvertently. The abacus is mainly used for adding, subtracting, multiplying, dividing, square rooting and cube rooting. Although my grandfather has retired from being a shop owner, he practices the abacus in his free time and use it in his daily live.