Model railroad type example Sn3.5 is as follows, S (scale) being the prefix to n (narrow gauge) followed by 3.5 (prototype track gauge in feet), 3 and 1/2 feet, or 42 inches, which in Sn3.5 equates to actual modeling track width of .649 - .672 thousandths, 16.5 - 17.1 mm.
Definition of harmonic. 1  1a : overtone; especially : one whose vibration frequency is an integral multiple of that of the fundamentalb : a flutelike tone produced on a stringed instrument by touching a vibrating string at a nodal point.
A fundamental vibration is excited when one such quantum of energy is absorbed by the molecule in its ground state. When two quanta are absorbed the first overtone is excited, and so on to higher overtones. To a first approximation, the motion in a normal vibration can be described as a kind of simple harmonic motion.In this approximation, the vibrational energy is a quadratic function (parabola) with respect to the atomic displacements and the first overtone has twice the frequency of the fundamental. fundamental vibration is excited when one such quantum of energy is absorbed by the molecule in its ground state. When two quanta are absorbed the first overtone is excited, and so on to higher overtones. To a first approximation, the motion in a normal vibration can be described as a kind of simple harmonic motion.