Figure 24  Graph showing the relative strength of flat-back, rectangular, and rounded rails. Results are generalized using the dimensionless parameter w/t where w is rail width and t is rail vertical thickness. The flat-back arm rail of the chair illustrated in fig. 8 is 1.004" wide and .612 " thick; its w/t ratio is 1.639 and its relative strength ratio is 1.275, making it about 27.5% stronger than a rounded rail of the same size. Had its rail been rectangular, it would have been about 43% stronger than a rounded rail of the same size.