The thickness of the lines depends on the distance from the benchmark, which is the cross-hair on the RRG. The cross-hair is also known as the origin where the x-axis (RS-Ratio) crosses the y-axis (RS-Momentum). Thicker lines will be further from the benchmark, and thinner lines will be closer to the benchmark. The further a security is from the benchmark, the bigger the move in relative performance (up or down). The closer a security is to the benchmark, the smaller the move in relative performance (up or down). In other words, the thicker lines represent bigger moves and the thinner lines represent smaller moves.