anchor.diff:      record_batch(Start, End, Events),
       {reply, ok, State};
   
  +handle_call({event, Duration}, _From, #state{}=State) ->
  +    record_event(Duration),
  +    {reply, ok, State};
  +
   handle_call(experiment_started, _From, #state{}=State) ->
       record_experiment_started(),
       {reply, ok, State};
  
positive.code: -spec batch(term(), term(), number()) -> ok | error().
  batch(Start, End, Events) ->
      gen_server:call(?MODULE, {batch, Start, End, Events}, infinity).
  
  -spec experiment_started() -> ok | error().
  experiment_started() ->
  
negative.code:     append_to_file(Filename, Line).
  
  %% @private
  record_event(Duration) ->
      Filename = main_log(),
      Timestamp = timestamp(),
      Line = get_line(event, Timestamp, Duration),
      append_to_file(Filename, Line).
  
  %% @private
  record_batch(Start, End, Events) ->
      Filename = main_log(),
      Timestamp = timestamp(),
  