My PhD examiners have asked me to refer to equations using Eq. (6) rather than Eq. 6. This seems simple enough, but often I have sentences of the form:
"This is a fact related to an equation you passed many pages ago (see Eq. 6)."
To me it seems insane to rewrite this as:
"This is a fact related to an equation you passed many pages ago (see Eq. (6))."
What are the accepted ways of formatting the equation number in parenthetical references?