Sample

Before error handling is added:

Option Explicit

Private Sub Command1_Click()

sayHello
End Sub

Private Sub sayHello()

    MsgBox "Hello"
    ' now for an error
    Print 1 / 0
End Sub

After error handling and line numbers are added:

Option Explicit

Private Sub Command1_Click()

    On Error GoTo Error_Routine

    1   sayHello

Exit_Routine:
    Exit Sub
Error_Routine:
    Debug.Assert False
    Errorlog "Form1.Command1_Click"
    Resume Exit_Routine
End Sub

Private Sub sayHello()

    On Error GoTo Error_Routine

    1    MsgBox "Hello"
        ' now for an error
    2    Print 1 / 0

Exit_Routine:
    Exit Sub
Error_Routine:
    Debug.Assert False
    Err.Raise Err.Number, "Form1.sayHello(" & Erl & "):" & Err.Source, Err.Description
End Sub