The basic issue is a missing spaces. The minimum requirement is:
{IF{MERGEFIELD HR}> 80 {MERGEFIELD HR} {MERGEFIELD HR}}
You could also use:
{={MERGEFIELD HR}-80 \# "'{MERGEFIELD HR}';'{MERGEFIELD HR}'"}

Note: The field brace pairs (ie '{ }') for the above examples are created in the document itself, via Ctrl-F9 (Cmd-F9 on a Mac); you can't simply type them or copy & paste them from this message.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Thank you for your help. It now works just fine and dandy.