Speed Up Macro That Adjusts Row Height & Column Width

This used to (and on some machines still does) work very well, but all of the sudden on my work machine, it is incredably SLOW!! The whole program takes a list of tasks and dates, and creates a wall calendar from them. Then (the offending part, below in code) looks at each cell on the wall calendar and formats it by sizing the height of a merged cell so that the entire task is displayed, then goes on to put a square around it (works fine).

The formating of the cell height/width can take up to 11 SECONDS each cell. What is happening to do this? Again, it USED to, and on some machines still does, FLY through this process. But now it just crawls. Code below, with the 3 offending lines identified.

Private Sub Fit_Height(ByVal Target As Range)
Dim NewRwHt As Single
Dim cWdth As Single, MrgeWdth As Single
Dim c As Range, cc As Range
Dim ma As Range

Application. ScreenUpdating = False
With Target
If .MergeCells And .WrapText Then
Set c = Target.Cells(1, 1)
cWdth = c.ColumnWidth
Set ma = c.MergeArea
For Each cc In ma.Cells
MrgeWdth = MrgeWdth + cc.ColumnWidth
Next

An additional item (clue?) is that, after the macro is done running, it is still unbearably slow to do anything on-screen. Grabbing the column header and changing the column width takes 5 seconds or so before it snaps to the desired width and displays correctly. Closing Excel and reopening it takes care of that problem.

More advancement (as I wait). It seems to be the Application.PageSetup that kills it. As soon as I hit the first Application.PageSetup line, the app grinds to a halt, and almost every line after that that manipulates the screen format or the page format takes 5 or so seconds EACH to process. I put them all at the end, but that really doesn't solve the problem, nor explain it, nor give me a true solution.