The simple, rugged construction of this inexpensive apparatus has made it very widely used for elementary work. The apparatus consists of a heavy metallic base of size 50×10 cm with four vertical pillars. One supports a pointer, pivoted at its upper end, with the free lower end traversing on arbitrary scales. In the same pillar there is a supporting bracket for the specimen rod. The second pillar carries the arbitrary scales. The third pillar holds the brass rod from the center. The fourth pillar supports the second end of the specimen rod (brass rod) and has an adjustment screw for setting the pointer to zero. Dimensions of the brass rod are 12.5×5/32 inches.