Please have a look at @Jeeped's answer as it is the most efficient answer.
The Code below needs to be copied to every sheet module.
Private Sub Worksheet_Change(ByVal Target As Range)
Dim ws As Worksheet
If Target.Address = "$B$5" Then
For Each ws In ThisWorkbook.Worksheets
If Not ws.Name = Me.Name And Not ws.Name = "Sheet3" Then
If Not ws.Range(Target.Address) = Me.Range(Target.Address) Then
ws.Range(Target.Address) = Me.Range(Target.Address)
End If
End If
Next ws
End If
End Sub
This is fairly easy with activeX comboboxes on the sheets
On the workbook module add the code below to populate the comboboxes
Private Sub Workbook_Open()
With ThisWorkbook
With .Worksheets("Sheet1").ComboBox1
.AddItem "Complete"
.AddItem "Incomplete"
End With
With .Worksheets("Sheet2").ComboBox1
.AddItem "Complete"
.AddItem "Incomplete"
End With
End With
End Sub
On the "Sheet1" Module add
Private Sub ComboBox1_Change()
If Me.ComboBox1 = "Complete" Then
ThisWorkbook.Worksheets("Sheet2").ComboBox1.Value = "Complete"
ElseIf Me.ComboBox1 = "Incomplete" Then
ThisWorkbook.Worksheets("Sheet2").ComboBox1.Value = "Incomplete"
End If
End Sub
On the "Sheet2" Module add
Private Sub ComboBox1_Change()
If Me.ComboBox1 = "Complete" Then
ThisWorkbook.Worksheets("Sheet1").ComboBox1.Value = "Complete"
ElseIf Me.ComboBox1 = "Incomplete" Then
ThisWorkbook.Worksheets("Sheet1").ComboBox1.Value = "Incomplete"
End If
End Sub