I think the "they" is somebody else.. that's how I understand it.

When the user selects and displays a variable that (e.g. the people that run the program) want to monitor...

I don't know if it makes sense in your text.

I think it's the option for avoiding he/she:
When the user selects... a variable that they (the USER) want to monitor. I think the text includes this option in order to be more inclusive and not have to say: when the user selects... a variable that HE/SHE (i.e. the user) wants to monitor.

If it was PLURAL: "the users", then the verb would also have to change and it would read: when the users SELECT ... a variable that they want to monitor.

I can haphazard a guess about the context.

Visualise a psychological test. 'User' is a person undergoing a test on the computer. There is a set of 'people' monitoring the 'user'. When the user selects and displays a variable that the 'people' are monitoring in their study, then some xxx event is executed.

Alternatively, visualise an interactive TV scenario. The 'user' is a 'TV viewer'. The advt agencies are monitoring tv usage. When the viewer selects some item (icon?) on the TV through his remote clicks, some variable is set, which is trapped by the circuitry and passed on to the monitoring agency. If this variable is the one under study, then the xxx events are triggered.

Am i on track, or totally of the mark ? :-))

Regards,
Sanjay.

you will have troubles using a/the user, because after it will have to be referred to as he/she. You cannot use plural for users hence you cannot use they later on. your best bet is to turn the sentence around to render it passive so that you will not have to repeat user(s), he/she, they.
give us the sentence and i'll be able to help you

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Note added at 11 mins (2004-04-06 14:41:11 GMT)
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When the user selects and displays a variable that they want to monitor could become:
when a variable is selected and displayed for monitoring purpose, ...

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Note added at 21 mins (2004-04-06 14:51:43 GMT)
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in answer to user no: this is bad grammar as there is lack of agreement between subject (the user)and referrent (they)

Using "they/them" with a singular subject seems to become more common, but is grammatically incorrect. Besides, it can lead to misunderstanding, as some of the answers proved.

As Rita pointed out, the sentence can be rewritten to avoid the he/she issue. This is the preferred method in technical writing.
Make sure to use the active voice, though. Use of the passive voice does not improve the user's understanding.

In manuals, the issue can often be avoided by addressing the user directly, e.g. "Enter your password" or "You must provide your password"**. In a brochure, this is not always possible, since the reader is not necessarily the end user.

If a workaround is not possible, the author can use a plural subject, e.g. "If users are confused, they should read about error messages".** This would also be an option for the sentence Klaus is struggling with. There's nothing wrong with "When users select and display a variable that they want to monitor...", except that it sounds slightly more stilted than Rita's suggestion.

Finally, some additional piece of advice from The Complete Idiot's Guide to Technical Writing: "Save "he or she" for times when there really is no other good alternative--then use it without guilt. Occasional use won't trip up the user. The most challenging part of nonsexist writing is simply raising your own awareness about it. Once that's done, incorporating it becomes easier and more natural".

** Examples marked with ** were also taken from The Complete Idiot's Guide to Technical Writing (Alpha Books, 2001).