在规范场理论中规范不变的量被赋予物理意义，而规范依赖的量被视为多余的数学对象．既然如此，为什么规范仍在现代物理中广泛应用呢？Rovelli依据对一些具体规范场的分析，给出的1种解释是规范场间的耦合需要规范依赖量来描述．电磁场是1种最简单的规范场，它的自由场拉格朗日量可以用规范不变的相对广义坐标描述．两种理想介质的电磁场在界面的相互作用可以用两个场的相对广义坐标差表示．为保持该作用的规范不变性，两个场的规范函数必须与时间无关，并且梯度相等．

 In gauge field theory, gauge invariant quantities are endowed with physical meaning, while gauge dependent quantities are regarded as redundant mathematical objects. In that case, why are gauges still widely used in modern physics? Based on the analysis of some specific gauge fields, Rovelli gives an explanation that the coupling between gauge fields needs to be described by gauge dependent quantities. Electromagnetic field is the simplest gauge one, and the Lagrangian of free field can be described by gauge invariant relative generalized coordinates. The interaction between the electromagnetic fields of two ideal media at the interface can be expressed by the relative generalized coordinate difference of the two fields. In order to preserve the gauge invariance of this action, the gauge functions of the two fields must be time independent and their gradients are equal．