Convert units based on cell format

[Redrum555]

Hi everyone,

I've wrote this code that allow the user to enter data either in mm or inch and to be converted in the corresponding cell:

Private Sub Worksheet_Change(ByVal Target As Range)
Dim i As Integer

Application.EnableEvents = False

If Not Application.Intersect(Target, Range("G6:G19")) Is Nothing Then
    For i = 6 To 19
            Cells(i, "I").Value = Cells(i, "G").Value * 25.4   
    Next i
End If

If Not Application.Intersect(Target, Range("I6:I19")) Is Nothing Then
    For i = 6 To 19
            Cells(i, "G").Value = Cells(i, "I").Value / 25.4
    Next i
End If

Application.EnableEvents = True

End Sub

The issue I'm facing, is that some of the cells in the range should not be concerned by the conversion (other unit or with no unit at all).

So I'd like to edit the code to select the entire column and just ovoid the cells that do not have the right format ("0.0 in" and "0.0 mm")...

I cannot figure out a way of ignoring the cells with a different format.

Thanks in advance for your help.