Excel's precision is 15 significant decimal digits. You can use numbers that are much larger, but the precision remains 15 digits.
There are several add-ins available that have more precision, but then you can't use any of the results in the standard Excel
functions.
Here's one:

http://precisioncalc.com:80/

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Kind regards,

Niek Otten
Microsoft MVP - Excel

"ACRhyne" wrote in message ...
|I would like to do calculations in my spread sheet with 30 digits precision.
| I figure this is possible because the number display allows 30 digits. I went
| through the help function, and selecting the Precision as Displayed option
| under the Tools, Options, Calculation tab make no difference. Excel still
| rounds off at 12 digits. How do I get higher precision calculations?