In most cases, field coding can be used to manage the updating of linked fields - all you need do to ensure they're updated is to check the corresponding formfields' 'calculate on exit' property. In a similar vein to the previous link, to see how to do a wide range of calculations in Word, check out my Microsoft Word Field Maths Tutorial, at:
http://windowssecrets.com/forums/sho...Maths-Tutorial
or:
http://www.gmayor.com/downloads.htm#Third_party
Given that you're using formfields, you need to be aware of a calculation bug with them that this tutorial also discusses.
BTW: There is no code in the document in your attachment, so it's not possible to comment on any issues your code might have.