Hi Malcolm and welcome to our community
I'm sure there are maybe several ways to do it. Here is how I
would.
1. Define the variable.
2. Edit the TOC.
3. Where you type the verbiage of what the user sees in the
TOC, below that is a field labeled "Available Variables". You click
where you want the variable to be inserted (possibly before, after
or in between some text) select the variable (if you have more than
one) and click the Add button.
4. Poof! Your variable is inserted.
Cheers... Rick