If your input data starts in A1 and you'll allow a 'helper' column B...
In B2: =IF(ISNUMBER(A1),B1,A2) <-- this tracks the value to subtract
In C2: =IF(ISNUMBER(A2),A2-B2,"NA") <-- this becomes your result
--Bruce

"gtslabs" wrote:

The result is in the right hand column.
Thanks
Steve