# Calendar Types

Seth Kurtzberg seth at cql.com
Mon Feb 14 16:11:03 EST 2005

```Glynn Clements wrote:

>Bayley, Alistair wrote:
>
>
>
>>>You also need to specify, or let the user specify, the order of
>>>arithmetic.  I.e. adding a day and then a second is different from
>>>doing it the other way around.
>>>
>>>
>
>Only when leap seconds are involved. A month and a day would be a
>better example.
>
>
>
>>Duration arithmetic is not commutative? Can you give some examples please,
>>because I'm not able to imagine any.
>>
>>
>
>	April 30th + 1 month + 1 day = May 30th + 1 day = May 31st
>	April 30th + 1 day + 1 month = May 1st + 1 month = June 1st
>
>
What reason is there to say May 30 + 1 day == May 31st?  May 30 + 1 day
= June first.  So the answer is the same either way, as long as your
result for May 30 + 1 day is correct.

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