Hi Sheila,
You mention the filling in of a form, so I'll assume you're using a
formfield. In that case, all you need to do to set a bookmark for the
formfield and to make any dependent calculations update automatically is to:
1) Right-click on the formfield and select 'properties';
2) Check the 'calculate on exit' box; and
3) If you need to use the formfield's value outside a table, give it an
appropriate bookmark name instead of the default Word one (typically Text1,
Text2 etc).
Then, create the formula field that does the calculations.
Once that's done, simply protect the document for forms. from then on,
entering a value into the formfield then tabbing out of it will update the
calculation.
Cheers
PS: For more information on doing maths in Word, see:
http://www.wopr.com/cgi-bin/w3t/showthreaded.pl?Number=365442
(url all one line)