Documentation/How Tos/Calc: COUNTBLANK function
From Apache OpenOffice Wiki
COUNTBLANK
Returns the number of empty cells.
Syntax:
COUNTBLANK(range)
Returns the number of empty cells in the cell range range.
Example:
COUNTBLANK(A1:B2) | returns 4 if cells A1, A2, B1 and B2 are all empty. |