anchor.diff:  % multiplySeries
   evaluate_call(<<"multiplySeries">>, Series, _From, _Until, _Now) ->
       {Norm, _Start, _End, _Step} = normalize(Series),
  -    zip_series(Norm, fun safe_multiply/1);
  +    zip_series(Norm, fun safe_multiply/1, "multiplySeries");
   
   % nPercentile
   evaluate_call(<<"nPercentile">>, [Series, N], _From, _Until, _Now) when is_number(N) ->
  
positive.code:     with_function_name(pseudo_series(Values), Func).
  
  
  derivative_test_() ->
      [?_assertEqual([], derivative([])),
       ?_assertEqual(pseudo_values([null,null,1,1,1,1,null,null,1,1]),
  
negative.code:     end.
  
  
  zip_series([], _Func, _Name) -> [];
  zip_series([Hd | _] = Series, Func, Name) ->
      Values = lists:map(fun(#series{values=Vs}) -> Vs end, Series),
      % we use the first series as a template
      Zipped = Hd#series{values=zip_lists(Values, Func)},
      [with_function_name(Zipped, Name)].
  
  
  safe_sum(Vs) ->
  