Equations may be unnumbered, all numbered, or only numbered when cross-referenced. Always number sequentially. For long works, equations may be numbered by chapter. Usually, the numbers are in parentheses and right-aligned:
\begin{equation}\mathrm{~~~~~~~~~~~~~~~~} F_{hkl} = \sum_{j=1}^N f_j e^{-2\pi{}i\left(hx_i+ky_i+lz_i\right)} \mathrm{~~~~~~~~~~~~~(2)}\end{equation}
\begin{equation}\mathrm{~~~~~~~~~~~~~~~~~~~~~~~~}W = Fd\cos\theta \mathrm{~~~~~~~~~~~~~~~~~~(3.2)}\end{equation}
When presenting a sequence of equations as a block, the following options exist:
- All equations have their own numbers.
- The sequence is given a single number.
- Only the final result is numbered.
- The equations in the sequence have numbers of the form (2a), (2b) and so on.
Cite an equation in the text using a capital letter followed by the number; do not enclose the number in parentheses:
Equation 2 Equations 2–4
Refer to Equation 2.
Check the style guide of the publication you are writing for, and think about your own cross-referencing needs.
