It is a separator between the sheet name and the cell address... and I
suspect your formula should look like this:

=IF(O2="carports",'input data'!$BX2*1000,"ERROR")



--
Steve

"Luis" wrote in message
...
In the formula =If (02="carports,"'input data' ! $B*X2*1000,"ERROR" What
does the ! stand for in Formula