anchor.diff:  % diffSeries
   evaluate_call(<<"diffSeries">>, Series, _From, _Until, _Now) ->
       {Norm, _Start, _End, _Step} = normalize(Series),
  -    zip_series(Norm, fun safe_diff/1);
  +    zip_series(Norm, fun safe_diff/1, "diffSeries");
   
   % integral
   evaluate_call(<<"integral">>, [Series], _From, _Until, _Now) ->
  
positive.code: 
  % limit
  evaluate_call(<<"limit">>, [Series, N], _From, _Until, _Now) when is_number(N) ->
      lists:sublist(Series, N);
  
  % mostDeviant
  evaluate_call(<<"mostDeviant">>, [Series, N], _From, _Until, _Now) when is_number(N) ->
  
negative.code: % multiplySeries
  evaluate_call(<<"multiplySeries">>, Series, _From, _Until, _Now) ->
      {Norm, _Start, _End, _Step} = normalize(Series),
      zip_series(Norm, fun safe_multiply/1, "multiplySeries");
  
  % nPercentile
  evaluate_call(<<"nPercentile">>, [Series, N], _From, _Until, _Now) when is_number(N) ->
  