Ruler A and Ruler B are plastic rulers stuck on the lower plate, and their 0 points are on the same vertical plane. Ruler B is fixed on the bottom plate (10) and can slide in the track. The bottom plate (10) is pressed with five pieces of plywood. Taking the bottom plate (65438) as an example, calculate 4+6= 10. First, move the handle B to the right to 4cm directly below the ruler B, and the pointer B indicates 4cm, and then determine the addend position; Then, move the handle A on the ruler A to the right along the sliding groove B to just below 6 cm, and then determine the addend position. At this time, the pointer A on the handle A indicates that the position on the ruler B is 10 cm, and the sum of addend and addend is determined.