I'm irritated by the ways in which Excel2002 SP3 mangles very large
numbers, both when importing them and when manipulating them.
I receive astronomical event data in .csv files, with one field
representing Unix time, seconds since epoch, measured to 10-
nanosecond resolution, i.e. SSSSSSSSSS.ssssssss. When this data is
imported, it's truncated (i.e. it becomes SSSSSSSSSS.sssss, losing 3
decades of resolution), UNLESS the field is defined as a TEXT field
during importation. Why, oh why would anyone do that, given that the
data is [by definition] comma-delimited? And what on earth goes
wrong when I subtract one value from another to derive elapsed time?
Consider:

A2 = 1147718110.21928262
A3 = 1147718110.21979061

(A3 - A2).VALUE yields 0.00050998
AH, BUT....
right(a3,10)-right(a2,10) yields 0.00050799
and Microsoft's calculator yields 0.00050799 .....

The moral? If you work with large numbers (and they don't have to be
Unix time), be very wary....