Once you have calculated error, see previous posts, the question becomes how to display the error limits. One way is to use error bars.
If you input ''how do I display error bars?" to answers.com, you get back ten hits to built-in answers and many web hits.
Among the web hits is:
Science Fair - How to Create a Winning Display:
(Note: The section on "Error Bars" can be found at the bottom of the page)
No doubt, this page is of general interest beyond this topic!
So plenty to research, hopefully your answer is in there.