anchor.diff:  
   datetime_to_utc({{Year, Month, Day}, Time}) ->
     BaseDate = calendar:datetime_to_gregorian_seconds({{1970, 1, 1}, {0, 0, 0}}),
  -  (calendar:datetime_to_gregorian_seconds({{Year, Month, Day}, Time}) - BaseDate) * 1000.
  +  (calendar:datetime_to_gregorian_seconds({{Year, Month, Day}, Time}) - BaseDate) * 1000000.
   
   
   
  
positive.code: -export([
    iso8601_to_utc/1,
    utc_to_iso8601/1,
    format/2,
    parse/2
  ]).
  
negative.code: 
  utc_to_datetime(Milliseconds) when is_integer(Milliseconds) ->
    BaseDate = calendar:datetime_to_gregorian_seconds({{1970, 1, 1}, {0, 0, 0}}),
    Seconds = BaseDate + (Milliseconds div 1000000),
    {{Year, Month, Day}, Time} = calendar:gregorian_seconds_to_datetime(Seconds),
    {{Year, Month, Day}, Time}.
  