Dim StateCount As Integer

Sub Convert()
    'This procedure toggles the case of text in Excel Cells
    
    Dim Cell As Range
    
    For Each Cell In Selection.Cells
    
        If Left(Cell.Formula, 1) <> "=" And Not IsDate(Cell.Value) Then 'Don't touch formulas or dates
            
            Select Case StateCount
                Case 0
                    Cell.Formula = StrConv(Cell.Value, vbProperCase)
                Case 1
                    Cell.Formula = StrConv(Cell.Value, vbUpperCase)
                Case 2
                    Cell.Formula = StrConv(Cell.Value, vbLowerCase)
            End Select
        
        End If
        
    Next Cell
    
    StateCount = StateCount + 1

    If StateCount = 3 Then StateCount = 0

End Sub