Path: utzoo!utgpu!watserv1!watmath!att!cbnewsb!druhi.att.com!neal
From: neal@druhi.att.com (XGPB30000-McBurnettND(DR9225)289)
Newsgroups: comp.sys.handhelds
Subject: Re: time formats for HP28s
Message-ID: <660@cbnewsb.ATT.COM>
Date: 25 Jul 90 20:27:27 GMT
References: <920@ncrwat.Waterloo.NCR.COM>
Sender: news@cbnewsb.ATT.COM
Reply-To: neal@druhi.ATT.COM (Neal D. McBurnett)
Organization: AT&T Bell Labs, Denver CO
Lines: 37

In article <920@ncrwat.Waterloo.NCR.COM>, jrl@images1.Waterloo.NCR.COM
(john Latala) writes:
|> Times are in the format HH.MMSSTT and dates are in the format MM.DDYYYY.
|> 
|> Sorting dates in the MM.DDYYYY format doesn't work! January 1, 1991
|> (01.011991) is before July 1, 1990 (07.011990)!
|> 
|> I was thinking about converting to something like YYYY.MMDD or even
|> YYYYMMDD.
|> 
|> After a bit more poking around I thought maybe going to a binary version
|> might be a litte neater, something like #YYYYMMDDhhmmssttd. This format
|> doesn't look to bad because I can get a complete date/time into one
|> number, which is kind of a nice idea.
|> 
|> In planning for when it happens how does the HP48 store/handle
|> dates/times?

Unfortunately, the HP48 also uses a date format which can't be sorted,
like the HP41, and even HP12.

I want the same characteristics you want:
	Both date and time in one object
	"<" operator works
I also want negative years to work (with the "historical" semantics in which
there is no year zero), and I want the precision to work down to fractions
of seconds.  [+-]YYYY.MMDDHHMMSS works pretty well except that some trailing
precision is lost.  The binary suggestion is interesting, but it is
more error-prone and tedious to enter (e.g. if you enter the wrong number
of digits).  I think your approach of using GMT is a good one, since problems
always come up with daylight savings time.

Another approach is to enter numbers via one scheme and store them in another,
e.g. enter as a complex (date, time) value and store as julian date (which
has precision down to around a second over the last 6000 years, as I recall.)

-Neal McBurnett // AT&T Bell Labs, Denver // neal@druhi.ATT.COM, att!druhi!neal