Thanks RedarEye. It works great!
I've also made the following change - because the input cell is a merged
cell (i.e. N13:O13), but Excel doesn't seem to allow ClearContents in a
merged cell when a cell (i.e. O13) is empty.

change:
Tartget.ClearContents

to:
ThisWorkbook.Worksheets("Sheet1").Range("N13").Cle arContents


"Target.ClearContents"

"RadarEye" wrote:

Hi Sam,

Try this:

' Begin of code ------------------
Private Sub Worksheet_Change(ByVal Target As Range)
If Target.Address = "$N$13" Then
If Not IsEmpty(Target) Then
If IsNumeric(Target.Value) Then
If Target.Value < 50 Or Target.Value 130 Then
MsgBox "Please enter a value between 50mm and
130mm.", vbOKOnly + vbInformation
Target.ClearContents
End If
Else
MsgBox "Please enter a value between 50mm and 130mm.",
vbOKOnly + vbInformation
Target.ClearContents
End If
End If
End If
End Sub
' End of code ------------------------

HTH,

Execurot