- Standardization serves to
- represent the most general case,
- reveal the simplicity of the essence,
- unify the various versions that have different appearances.

For the definition of density operator, [Pat, p.114, (7)] features the ensemble average; [Lan3, pp.38-41, §14] reveals its origin by considering a subsystem [Lan3, p.38, l.- 5]; [Coh, pp.300-301, Complement E_{III}, 4.a] puts it in the standard form. Pathria’s version and Landau’s version are special cases of Cohen-Tannoudji’s version [Coh, p.303, Comment (i)].

- [Mer2, p.31, l.-9-l.-7]

If a position wave function is normalized, its Fourier transform will also be normalized [Ru2, p.200, Theorem 9.13(b)]. Furthermore, the normalization is preserved at all times.

- (Estimation of self-inductance for simple circuits) Once a standard model [Jack, p.217, Fig. 5.21] is established, the nonstandard cases can be derived from the model easily [Jack, p.218, l.7-l.15].