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From: rrd@hpfcso.HP.COM (Ray Depew)
Newsgroups: comp.sys.handhelds
Subject: Re: HP-38E
Message-ID: <7360023@hpfcso.HP.COM>
Date: 9 Nov 90 00:46:51 GMT
References: <543@voodoo.UUCP>
Organization: Hewlett-Packard, Fort Collins, CO, USA
Lines: 57

Tom Mackey asked:  (among other things...)

+    How do you use the Delta-DAYS and DATE keys?
+
+    What is %T?  (This is probably a stoopid question, but what
+    the hey!)

Guessing here, based on bad memories of my junior year:

HP calculators use a date format of mm.ddyyyy, where today's date would
be 11.081990 .  In the 41 series, you could set a flag to reverse the dd and
mm; I don't know if the 38 will allow that.

AT ANY RATE:  to use the Delta-DAYS function, put one date in y and one date
in x, in the mm.ddyyyy format.  The calc should return the number of days
between the two dates, to the X-register.  (Also known as the "days-between-
dates" function.)

To use the DATE function, put a date in mm.ddyyyy format in the X-register.
It will be replaced with an integer from 1 to 7 denoting the day of the week
that that date falls on.  I think 1 = Sunday, 7 = Saturday, but I wouldn't
bet my job on it.  Try it first.

%T is a useful function.  It stands for "percent total."  Put your TOTAL
in y, and your SUBTOTAL in x.  The machine leaves the "percent of total"
in x, the TOTAL remains in y, and stack-lift is disabled.  This presents
two possibilities:

a) To calculate more %T's, you don't need to re-enter the TOTAL. Just 
enter a new subtotal and hit [%T] again.  You can repeat this as long as
you wish, because stack-lift remains disabled.

b) To recover your original SUBTOTAL, hit plain old [%].  "Percent" takes
the TOTAL in y and the PRECENTAGE in x, and returns the SUBTOTAL in x, the
TOTAL still in y, and the stack-lift disabled.  For this reason, you can think
of %T and plain-old-% as inverse functions of each other -- that is, the one
"undoes" the other.

The HP-41 series didn't have a %T function, so many users created an equivalent
program:

01	LBL "%T:
02	1/X
03	%
04	1/X
05	END

and assigned it to the shift-% key, so it was only a USER-key away.

I'm wearing my ironclad underwear while posting this.  I don't officially 
represent HP, and what I say may or may not work.  But heck, it doesn't hurt
to try.

Have fun.

Ray
rrd@hpfitst1.hp.com