You can achieve this numbering, but it can't be entirely "automatized" without losing some of Word's built-in facilities. Initially, I'm just going to try to address the specific situation that you have described, i.e. you sometimes want *two* successive equations labelled with the same number but with A for the first and B for the second. If you are actually looking for something more general than that, e.g. you might have A,B,C or the related equations are not necessarily immediately after one another,

- You may need a more complex scheme and
- You will need to describe your requirement in more detail and think about whether you are willing to lose certain Word features.

Normally, if you define a Caption label "Eqn." and use chapter.caption numbering with (say) Heading 1 style paragraphs as your headings, Word will use the following text and field coding to insert your captions

```
Eqn. { STYLEREF 1 \s }.{ SEQ Eqn. \* ARABIC \s 1 }
```

(Where all the { } are the special field brace pairs that you can insert on Windows desktop Word using ctrl-F9).

Maybe you are inserting brackets manually around the caption like this

```
(Eqn. { STYLEREF 1 \s }.{ SEQ Eqn. \* ARABIC \s 1 })
```

but let's leave that aspect to one side for now.

AIUI what you want is to be able to have a sequence of equations numbered like this

```
Eqn. 1.1
Eqn. 1.2A
Eqn. 1.2B
Eqn. 1.3
```

So at first sight you could achieve that by modifying the caption for 1.2A to be like this

```
Eqn. { STYLEREF 1 \s }.{ SEQ Eqn. \* ARABIC \s 1 }A
```

and the caption for 1.2B to be like this

```
Eqn. { STYLEREF 1 \s }.{ SEQ Eqn. \* ARABIC \c }B
```

because the `\c`

option just says "use the current number in the `Eqn.`

sequence"

*But*, if you have created your Table of Eqn.s in the usual way (by inserting a Table of Figures and selcting the Label `Eqn.`

), it won't actually pick up the 1.2B caption, because it just does not recognise a SEQ field with a `\c`

option.

One way to fix that is to apply a specific paragraph style (say, "Eqn" to your Equation captions, and generate your Table of Equations using that.

Another is to modify the code for the A and B captions so that the Table of Eqns. The most obvious possibility is:

```
Eqn. { STYLEREF 1 \s }.{ SEQ Eqn. \* ARABIC \s 1 }{ SET XEQn { SEQ Eqn. \c } }A
Eqn. { STYLEREF 1 \s }.{ SEQ Eqn. \* ARABIC \r { XEQn } }B
```

For two equations A and B it doesn't really make sense to try to generate the A and B using any kind of { SEQ } numbering. If you do, the first SEQ typically has to reset the sequence using `\r 1`

and the second one does not. But it is no simpler.