gistfile1.hrl

to_tz(R, Tz) ->
    Tz_offset = ((Tz#timezone.hour * 60) + Tz#timezone.minute) * 60,
    R_offset = (((R#timestamp.timezone)#timezone.hour * 60) + (R#timestamp.timezone)#timezone.minute) * 60,
    R_seconds = calendar:datetime_to_gregorian_seconds(to_datetime(R)),
    New_seconds = R_seconds - R_offset + Tz_offset,
    Datetime = calendar:gregorian_seconds_to_datetime(New_seconds),
    {ok, New_R} = from_datetime(Datetime),
    New_R#timestamp{timezone = Tz, fraction = R#timestamp.fraction}.