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NOTE: Unfortunately, most physics textbooks and simulations adopt the definition of flux as âˆ«E.dA. On the other hand, the alternative definition (∫D.dA) used in electrical engineering and adopted in Understanding Physics — see footnote on page 377 of the text — is generally simpler, makes the study of electromagnetism more internally consistent and conforms to the conventions of the International Union of Pure and Applied Physics (IUPAP). 

It is important to realise, however, that this issue has no impact on subsequent material since the definitions of the quantities D and E are the same in all formulations of electrostatics.

For more clarity on the issue see the  Section y.