I am using the following code to put the current time in column c when I type
a riders number into column a. What I would like to be able to do is to
change the code so that if there is already a value in column a, I can change
it (like in the case of a typo that needs fixing) I can without the time
getting updated again.

Private Sub Worksheet_Change(ByVal Target As Range)
If Not Application.Intersect(Target, Columns("B:B")) Is Nothing Then
Target.Offset(0, 1).Value = Format(Now, "h:mm:ss")
End If
End Sub

Thanks again.