anchor.diff:  %  Sign = term(), '+', '-'
   %  Hours = Minutes = Integer(),
   %  {Shift, DstShift} - returns, when shift is ambiguous
  +%  ErrDesc = atom(), unknown_tz
   tz_shift(_UtcDateTime, "UTC") ->
      0;
   tz_shift(LocalDateTime, Timezone) ->
  
positive.code:          end
     end.
  
  tz_shift(LocalDateTime, TimezoneFrom, TimezoneTo) ->
     FromShift = fmt_shift(tz_shift(LocalDateTime, TimezoneFrom)),
     DateTimeTo = localtime:local_to_local(LocalDateTime, TimezoneFrom, TimezoneTo),
     ToShift = fmt_shift(tz_shift(DateTimeTo, TimezoneTo)),
     fmt_min(ToShift-FromShift).
  
  adjust_datetime(DateTime, Minutes) ->
     Seconds = calendar:datetime_to_gregorian_seconds(DateTime) + Minutes * 60,
  
negative.code: %  LocalDateTime = DateTime()
  %  TimezoneFrom = String()
  %  TimezoneTo = String()
  %  ErrDescr = atom(), unknown_tz
  local_to_local(LocalDateTime, TimezoneFrom, TimezoneTo) ->
     case local_to_utc(LocalDateTime, TimezoneFrom) of
        Date = {{_,_,_},{_,_,_}} ->
  