I started thinking about this question because of this discussion:
http://sbseminar.wordpress.com/2010/08/10/negative-value-added-by-journals/
about how journals often change a paper (for the worse) after acceptance.
Here's my question: Since it doesn't make sense to number every single equation (especially if you will only refer to it once in the text), I often use the phrase "the equation above" or "the equation below" to refer to the previous or next displayed equation. I am well aware that after compiling, said equation may be on the previous or next page, respectively, and not strictly above or below. I thought this was common practice. One journal publisher changed every single one of my "the above equation" phrases to "the earlier equation". I didn't bother protesting, but in my mind it definitely made the text worse.
Do other people avoid using "above" and "below"?
Best Answer
I used to number only equations I referred to, but then someone pointed out the following. When you write a paper and make it public, you are de facto allowing other people to talk about your paper and simply because you in your paper see no reason to refer to some equation does not mean that other people reading your paper will not do so. Hence as a friendly gesture to your readers, you should number all your equations, and in this way allow them to refer to, say, equation (n) in your paper, instead of having to come up with some complicated reference. Since that time I have tried to number all my equations.