Maybe something like:
Dim myRng As Range
With Sheet1
Set myRng = Union(.Range("clr1"), .Range("clr2"), .Range("clr3"))
End With
myRng.Replace what:=0, replacement:="=Na()", _
lookat:=xlWhole, searchorder:=xlByRows, MatchCase:=False
(I got lazy and stopped after clr3.)
> Could this be shortened to one block with something like, ("clr1",
> "clr2", ..). Taking it a step further, could the block be replaced
[quoted text clipped - 16 lines]
> If cell = "0" Then cell.Formula = "=NA()"
> Next cell

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Dave Peterson