Since XL only calculates to 15 digits, you can use longer data, such as
credit card numbers, by either *pre-formatting* the cell(s) as TEXT, or
precede the data with an apostrophe [ ' ], which will not be visible in the
cell, but can be seen in the formula bar.

--
HTH,

RD

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toolb" wrote in message
...
last number of 16 is 1 but automatically changed to zero. why