Private Sub Worksheet_Change(ByVal Target As Range)
'Check if the user made a change in col B
If Intersect(Target, Range("B:B")) Is Nothing Then Exit Sub
'Check if multiple cells were affected. Might be able to handle this,
'but for now we'll ignore
If Target.Count > 1 Then Exit Sub
'turn off the triggers, since our code is about to make a
'change to the worksheet and we don't want to trigger
'another event. =P
Application.EnableEvents = False
'Clear the cell from col A in the target's row
Cells(Target.Row, "A").ClearContents
'turn trigger back on
Application.EnableEvents = True
End Sub