In physics, the magnitude (length) of a vector is a scalar in the physical sense, i.e. a physical quantity independent of the coordinate system, expressed as the product of a numerical value and a physical unit, not just a number.
A pattern of multiple resonance's (spectral lines) observed when the initially single Larmor frequency of a given nucleus in a spin system is split by interactions with neighboring spins through the scalar or spin spin interaction. The magnitude of this interaction is independent of the applied magnetic field and is referred to as J, the spin spin coupling constant. The specific pattern produced depends on the number of coupled nuclei and their spin quantum numbers.