The method for calculating Flory's solvent swelling parameter often appears to differ from book to book. This lowers the quality of understanding of this model to such an extent that it seems pertinent to go back to the basics and review how Flory reasoned out this famous expression. By so doing, it is hoped that the reader will see how this model fits in the framework of the Van der Waals gas equation and the more general virial expansion of the gas equations. We only endeavor to hit on the flow of the concepts and only briefly at that, so the interested reader is advised to consult the literature for detailed information.