Hi Dave. No offense taken (in either chain).  I think I've made my position clear - calendar based intervals. Otherwise 1 year would be 365 days (or worse 365.25 days).  So 2 days from now is actually only 47 hours off not 48. 

If you want  3 intervals of 24 hours I'd propose using 3 * 24 hours instead. 

Yes my answer doesn't solve every thing. But it is useful in certain areas - common areas. It does need better documentation though. 

-cbc

Sent from my iPhone

> On Mar 7, 2015, at 4:14 PM, David T. Lewis <lewis at mail.msen.com> wrote:
> 
>> On Fri, Mar 06, 2015 at 09:10:13PM -0800, Chris wrote:
>> 
>>>> On Mar 6, 2015, at 5:00 PM, David T. Lewis <lewis at mail.msen.com> wrote:
>>>> 
>>>> On Fri, Mar 06, 2015 at 11:52:04PM +0000, commits at source.squeak.org wrote:
>>>> A new version of KernelTests was added to project The Inbox:
>>>> http://source.squeak.org/inbox/KernelTests-cbc.291.mcz
>>>> 
>>>> ==================== Summary ====================
>>>> 
>>>> Name: KernelTests-cbc.291
>>>> Author: cbc
>>>> Time: 6 March 2015, 3:52:01.005 pm
>>>> UUID: 54afce93-39e9-4c4a-92a4-ecbe32540c69
>>>> Ancestors: KernelTests-ul.290, KernelTests-cbc.278
>>>> 
>>>> Added DateAndTimeArithmeticTest - to test adding things to DateAndTime instances.  This includes things like: DateAndTime now + 3 days.
>>> 
>>> This would be a good time to check our tests. In my locale, the springtime
>>> daylight savings time change is going to happen this weekend. If I evaluate
>>> "DateAndTime now + 3 days" what is the expected result?
>> 
>> It should be three days from now, same hour of the day I think.  That was not part of the tests, though. Something to add. 
>> 
>> This change is part of a set ( including new kernel and be collection packages ). Adding days though was not changed. 
>> 
> 
> Hi Chris,
> 
> My comment was not meant as a criticism of your changes, it is more a
> general observation about our murky definitions of time in Squeak.
> 
> If "3 days" means a duration of 259200 seconds, and if the time in my
> (Detroit) time zone right now is 2015-03-07T18:00:00-05:00 (6:00 pm),
> then the DateAndTime that I should see three days from now is
> 2015-03-10T19:00:00-04:00 (7:00 pm, 259200 seconds from now).
> 
> On the other hand, if "3 days" means three calendar days (as I think that
> you are expecting it to mean), then the DateAndTime three days from now
> would be 2015-03-10T18:00:00-04:00 (still 6:00 pm on the wall clock, but
> actually an hour earlier in terms of elapsed time).
> 
> These are two different points in time, separated by 3600 seconds of
> actual duration.
> 
> So conceptually, we need to agree if "3 days" is a duration, or if it is
> a count of days on the calendar. The current implementation of "3 days"
> in Squeak implies that we mean it to be a duration (259200 seconds). If
> that is the case, then thinking of "3 days" as an count of calendar days
> is not the same thing at all, and the question "what DateAndTime will it
> be be 3 days from now" is ambiguous when a daylight savings transition
> is involved.
> 
> The daylight savings time transition illustrates the problem nicely, but
> IMO the real issue is lack of clear definitions of what we mean by words
> like "day" and "month" and "year". In everyday spoken language, it is OK
> for those words to have different meanings in different contexts. But
> even Squeak is not smart enough to resolve those ambiguities without a
> little help from us :)
> 
> Dave
> 
>