Excel handles only 15 digits until it loses values due to rounding. If
you have a longer number, you can either format the cell as Text
(Format menu, Cells item, Number tab, choose Text) before entering the
data or precede the value with an apostrophe. The apostrophe will not
be displayed in the cell, but will be visible in the formula bar. Both
of these methods assume that you will not due calculations on the
number (as is the case with data such as credit card numbers) although
sorting and filtering will still work.
Cordially,
Chip Pearson
Microsoft Most Valuable Professional
Excel Product Group, 1998 - 2009
Pearson Software Consulting, LLC
www.cpearson.com
(email on web site)