1.  Dimensional analysis

Dimensional analysis is based on a simple principle of physics: the formulation of a physical phenomenon must be dimensionally homogeneous, i.e. its expression as a function of the parameters on which it depends must be independent of the chosen system of units, and the dimensions (in the sense of "units") attached to each monomial of the expression must be analogous to the dimension of the phenomenon. With the dimensions respected, any expression representing a physical phenomenon can be put into adimensional form. This adimensional form calls on the Vaschy-Buckingham theorem, also known as the π theorem.