I don't think there's a way to make CountIf work across multiple sheets. Here's two options that might work:
1) On sheet 255 create a list of links to each of the other sheet's cell A12 - so all of the values would be on one sheet. You could thenuse CountIf on this range.
2) Write your own function to do this. Add the following code to a code module in your workbook:
Function Count3D(aiFirstSheet As Integer, aiLastSheet As Integer, _
asCell As String, asValue As String) As Integer
'aiFirstSheet and aiLastSheet are the sheet numbers of the first and last sheets to check
'asCell is the cell address of the cell to check
'asValue is the value in the cell that you want to check for
' only cells that contain this value will be included in the count
Dim I As Integer
Dim iCount As Integer
'this causes Excel to recalculate the function whenever the sheet recalcs
Application.Volatile True
'loop through the sheets and check for the desired value in the specified cell
'you can use UCase() to make the check not case sensitive
For I = aiFirstSheet To aiLastSheet
If ActiveWorkbook.Worksheets(I).Range(asCell).Value = asValue Then
iCount = iCount + 1
End If
NextCount3D = iCount
End Function
In the cell that you want the count to be displayed in, enter:
=Count3D(1, 254, "A12", "yes")
Hope this helps.
