A crude way would be like this (example):

Say the input range is A1:A10-
-Select A2:A10.
-Data, Validation, and in the Allow drop down pick Custom.
-Enter the formula =A2A1
-Modify Error Alert if you want.

The effect is that each cell entry must be greater than the cell above.

--
Jim
"a-one-and-a-two" wrote in message
...
| We manually enter order numbers in one column of our spreadsheet, which
are
| usually, but not always sequential. Can I use validation to alert when
the
| next entered order number is NOTa sequential whole integer? Thanks for any
| assistance!