Bill, It's taken me a long time to understand this issue. Still haven't figured out a good solution. The effect is because of the observance of DST when it changes. The issue is that you are subtracting a constant from the date. Where DST is observed, 2 days out of the year are not 24 hours. In the statements below I will reference dates in the US but the concept is the same for any where that observes DST.
March 14th is a short day. That day is 23 hours in length. So 864000 is not exactly 10 days during that time period. 864000 translates to 10 days and 1 hour until after march 15th in your case. On November 7th this year you have the opposite effect. November 7th is a 25 hour day. 864000 would translate to 9 days and 23 hours until after November 17th. Hope this helps with the understanding of what is happening. Dave ________________________________ From: Action Request System discussion list(ARSList) [mailto:arsl...@arslist.org] On Behalf Of William Rentfrow Sent: Tuesday, March 02, 2010 12:03 PM To: arslist@ARSLIST.ORG Subject: Weird DST date calculation issue ** Fortunately this issue SHOULD be very straight forward. Unfortunately - it isn't. There's a button that calculates a person's period of eligibility to make changes to their HR benefits, etc. You enter their employment anniversary date and hit the button and this performs a calculation: $My Date$ - 864000 (i.e., minus 10 days). Here's the interesting thing - when the date entered is Daylight savings time - 3/15 this spring - the calculated value for the date time field returns 3/4/2010 11:00:00 PM. Normally all of the times in this date/time field are left at 12:00:00 AM and are unused. Technically speaking the calculation is EXACTLY correct. 3/4/2010 11:00:00 PM is exactly 10 days before 3/15/2010 12:00:00 AM - because 3/15 has an "extra" hour added that is a figment of our collective imagination. Technically DST doesn't happen until 2:00 AM though but that's a matter for another time. I was thinking about changing the times on these to default to 3:00:00 AM instead of 12:00:00 AM - but I'm open to suggestions. William Rentfrow Principal Consultant, StrataCom Inc. wrentf...@stratacominc.com Blog: www.williamrentfrow.com<file://www.williamrentfrow.com> O 715-592-5185 C 715-410-8056 _Platinum Sponsor: rmisoluti...@verizon.net ARSlist: "Where the Answers Are"_ _______________________________________________________________________________ UNSUBSCRIBE or access ARSlist Archives at www.arslist.org Platinum Sponsor:rmisoluti...@verizon.net ARSlist: "Where the Answers Are"
