Reynald's number
Interesting comments all.
Now put yourselves in the current application of RN:
Model aircraft and how the understanding of RN may help those in the hobby.
Simply stating that it is extremely technical and requires knowledge of sub contexts etc., is of little help to the modeler who just wants to know why his model flies differently, as compared to larger models.
As long as the idea of why is coveyed, it matters little how the idea is explained.
Empirical data ( my spelling!), can be used to show what the textbook tries to explain.
This isn't quantum mechanics-