"S" was the name given by the National Model Railroad Association (NMRA) in 1943 for modeling in a ratio of 1:64. Meaning, real-world (a.k.a. prototype) measurements are divided by 64 to provide the scale model dimensions. The scale is also known as "3/16th scale", because a prototype English foot is equal to 3/16 of an inch in S-scale. Conveniently, each 1/64" tick mark on a ruler represents a scale one inch on the model. S-scale has its roots in the American Flyer brand. Before World War II, A.C. Gilbert bought the American Flyer product line, and made trains that could operate on the Lionel O-scale track. The equipment was made to 1:64 scale, but the wheels and trucks were gauged to the O-scale standard. After WWII, to be able to better compete with rival Lionel, A.C. Gilbert developed the more prototypical-looking two-rail system, and spaced the rail gauge to that of S-scale (Lionel used a third rail down the center of the track, since it primarily used AC power for the engines). This text and scale photo is courtesy of the NASG organization, whose WEB site can be found at www.NASG.org.