It is when translating it into model terms that scale and gauge sometimes become intermixed or confusing. Perhaps the following table will help clarify the situation as well as demonstrating why the confusion arises from time to time. It shows the commonly used types of models followed by the track gauge that is normally used for models of that type when depicting standard gauge track. Following this are the two commonly used methods of describing the scale and, in brackets, the prototype track gauge that it translates into. However, the current standard is considered to be 18.2mm.
Several things become clear from the table.
First, the track gauge rarely comes out the same when using the two conversion methods, which is a demonstration of the previously mentioned compromises. Finally, apparently identical types of models are not in fact identical. A second example is HO models and OO models which also both run on the same track but which are modelled to different ratios and correpondingly different scales. It helps explain why a UK model in OO and a North American model in HO have about the same loading gauge when in reality they are quite different with the North American loading gauge being considerable bigger. It is this narrow gauge look of OO that led to the development of, EM and P4, which are modelled to the same ratio and scale as OO but run on track which is closer to the correctly scaled down version.