Scaling variables and dimensions

The concept of scaling dimensions is important in the physics of large systems, in particular, in the statistical mechanics of critical phenomena. The main purpose of this article is to explain and formulate this important concept in a more transparent and precise fashion. Discussion is in the framework of the $n$-component classical spin model and the renormalization group. It is emphasized that not every quantity, but only special ones, called scaling variables, have well-defined scaling dimensions. In general these variables can be derived by making use of certain parameters which are the scaling fields of Wegner. The dimensions are simply related to the exponents associated with the renormalization group. We hope to extract a fairly concrete picture by a general formulation followed by explicit determination of the scaling variables in the large-$n$ limit. Dimensions are obtained to $O\left(\frac{1}{n}\right)$.