The SI is a coherent system of units, but what does that mean?
N·m — newton meters — is an SI derived unit equivalent to kg·m2·s-2. There is, in fact, a special name for that SI derived unit: joule (J). But when a single SI unit corresponds to more than one quantity, there sometimes are naming conventions to distinguish them. Joules are used for energy, but torque (moment of force) is, by convention, expressed in N·m, and the photo shows the scale of a torque wrench.
