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From: silvert@cs.dal.ca (Bill Silvert)
Newsgroups: comp.sys.handhelds
Subject: Re: temperature conversion
Summary: What does the sum of two temperatures mean?
Message-ID: <1991Jan23.210957.7258@cs.dal.ca>
Date: 23 Jan 91 21:09:57 GMT
References: <2D042619A000047E@gacvx1.gac.edu>
Sender: silvert@cs.dal.ca.UUCP (Bill Silvert)
Reply-To: bill%biomel@cs.dal.ca
Organization: Habitat Ecology Div., Bedford Inst. of Oceanography
Lines: 29

In article <2D042619A000047E@gacvx1.gac.edu> U5513172@NMSUVM1.BITNET (Thomas L. Baca) writes:
>Hello fellow HP-users,   I have what may be a silly question, but I
>shall ask anyway.  WhenI add 25_'C ( read degree Celcius)  and 1_'F
>on my HP 48SX, I get an answer of 537.67_'F.  What terribly simple thing
>am I overlooking?  My wife tells me that the answer looks like Rankins
>(sp?).  Why is this happening?  I heard someone say that they asked HP
>about it and got a fix.  However, I don't really know if this guy knew
>what he was talking about.  I've never seen a reference to this
>phenomenom, so I'm inclined to believe that the problem is not really a
>problem.

What do you expect the sum of two temperatures to mean?  The HP48SX
doesn't know either.  So it converts the temperatures to the absolute
scale before adding them.  In other words, it converts 25'C to 298.15_K,
1'F to 256_K, adds them, and expresses the result in 'F.  But the result
doesn't mean anything.  The difference of two temperatures is of course
meaningful, and you can add two temperatures in order to average them,
but here you have to be careful: if you want to average 25'C and 1'F you
MUST convert to a common base, add them and divide by two.  The average
of these two temperatures is 39'F, which you don't get by dividing 538'F
by two -- you have to convert to absolute, divide by 2, and convert back
to F.  This is an inconsistency in the way the HP works.


-- 
William Silvert, Habitat Ecology Division, Bedford Inst. of Oceanography
P. O. Box 1006, Dartmouth, Nova Scotia, CANADA B2Y 4A2.  Tel. (902)426-1577
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