Re: Daylight Saving Time

Jeff,

Changing your system time zone from QN0500EST2 to QN0500EST will cause the
system to automatically recognize the start and end of DST.  As shipped by
IBM, DST will start at 2:00 local time on the first Sunday of April and end
at 2:00 local time on the last Sunday of October.

When DST starts local system time will change from 2:00 AM to 3:00 AM, and
when ending from 2:00 AM to 1:00 AM.  This will take place independent of
whether or not you are using an external time server, and will conform to
your local definitions of time.

Time adjustment is not used when changing local time for DST.  Time
adjustment is used when a discrepancy is detected between the UTC time sent
by the time server and the local UTC time maintained by the system.

Time adjustment is not used as that would cause the minute after 2:00 AM to
be "something" between 2:00AM and 3:00AM.  This time value (for example
purposes 2:01AM) does not exist (per your legislative authorities).  What
would the system convert that time to if you wanted to convert to Mountain
time?  What would an auditor say if a change was made at 2:01AM?  Likewise
a time value 2:01 after DST ended would imply an hour and a minute past the
DST time shift, not just one minute.

Users could use the time adjustment feature of the system to circumvent
this time shift for DST, but the system DST support is not going to start
recording 'non-existent' time stamps -- you'll have to explain this time
values yourself.  And using time adjustment by itself to make DST changes
(leaving the time zone unchanged) will cause discrepancies in the UTC
offset the system believes it's working in.

It is because of these types of headaches that the system internally tracks
time with UTC (rather than local time) starting with V5R3.  UTC does not
have the concept of DST.  Time simply moves forward, and the system then
converts the internal UTC times to the appropriate local times based on the
time zone in effect.  To avoid time shifts the use of a standard such as
UTC is the way to go.  Local times are just too easily changed by
government decisions.

Bruce Vining



                                                                           
             "Jeff Crosby"                                                 
             <jlcrosby@dilgard                                             
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I have never had to be concerned with this in the past, but the Indiana
legislature has now decreed that Indiana will begin observing DST this
year.

With the new time zone and especially time adjustment stuff available in
V5R3, I thought it would be simple:  change the system value QTIMZON from
QN0500EST2 to QN0500EST, the system will automajically start adjusting time
before DST starts/ends, and I'm good to go, but it doesn't look that
simple.

It doesn't look like 'time adjustment' takes place automatically at DST
start/end at all.  What I think happens is that because my i5 checks with
an
external time server every hour, the time will change in one fell swoop.
If
I _don't_ check with an external time server, it won't take place at all.

Assuming I have already changed to time zone QN0500EST, it sounds like I
need to:

1) On the Saturday before DST starts/ends, tell the i5 to stop checking
externally for the time.

2) Start a time adjustment either forward (spring) or backward (fall) 1
hour.

3) On Monday, tell the i5 to start checking externally for the time again.

Am I right?  Or missing something simple?

Thanks and I'll be moving to Arizona.

--
Jeff Crosby
Dilgard Frozen Foods, Inc.
P.O. Box 13369
Ft. Wayne, IN 46868-3369
260-422-7531

The opinions expressed are my own and not necessarily the opinion of my
company.  Unless I say so.


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