Note that activities and equilibrium constants are dimensionless numbers. The strength of electron phonon interaction is determined by the dimensionless coupling constant formula 1. The elements of the strain tensor are dimensionless (displacements divided by distances). Both the numerator and denominator of this ratio have dimension length squared (i.e. , dimensionless). The following equation gives a dimensionless specific speed. Any number of new dimensionless parameters can be calculated through exponents and multiplication. Hence "e" is defined as a dimensionless one-dimensional parameter. It is conjugate to the timelike polar angle , which is also dimensionless. Both express hardness as an arbitrary dimensionless number. It is proportional to the dimensionless fine-structure constant with no other dependencies. The mass number is a dimensionless quantity. Angles are, by convention, considered to be dimensionless variables. These should be chosen such that the dimensionless variables are all of order one. To nondimensionalize this, it must be rewritten as a function of a dimensionless variable. The same applies for other physical quantities which are not dimensionless.