Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!yale!mintaka!space.mit.edu!cmoore
From: cmoore@space.mit.edu (Christopher B. Moore)
Newsgroups: comp.sys.handhelds
Subject: HP48 units bug
Keywords: hp48, bug, units, UBASE, UFACT
Message-ID: <1990Sep19.024034.15518@mintaka.lcs.mit.edu>
Date: 19 Sep 90 02:40:34 GMT
Sender: daemon@mintaka.lcs.mit.edu (Lucifer Maleficius)
Reply-To: cmoore@space.mit.edu (Christopher B. Moore)
Organization: MIT Center for Space Research
Lines: 36


I have discovered what appears to be a previously unreported bug in my 
revision D ROMs.  The units application fails to properly handle units
with fractional powers.  The problem is easy to demonstrate by taking the
square root of 1_N (that's one Newton) and then trying to convert to base
units with UBASE.  The correct answer is, of course, 1_kg^.5*m^.5/s but the
calculator returns 1_kg*m/s.  The calculator does not handle fractional powers
of units, rather it simple rounds to the nearest integer power.  Another 
interesting result is that the UBASE of 1_N^.3333333 returns 1_1/s.  It appears
that UFACT calls UBASE because it suffers from the same bug. 

This bug has been independently verified on another D-ROM and an E-ROM.  I
called HP calculator support today (9/18).  I was told that they were
aware that the calculator behaves in this fashion and that the engineers
who designed it made a "concious decision" to round fractional powers of
units in order to make the calculator faster.  When I pointed out
to the person on the phone that the answer was WRONG, he agreed but said that
it was done so that the calculator would be faster.  When I told him that
fast calculators that give incorrect results are completely worthless, he
suggested that I simply type UBASE after every unit I enter.  That 
fixes the bug sometimes, but trying UBASE of 1_m^.5/s^.5 gives 1_m/s.  There
is no way around it other than to ignore the units application completely.

I find it astonishing that HP would conciously produce a computational device
that gives incorrect results and claim that it was done to promote speed of 
computation.  If you care about units, call HP (503-757-2004) and tell them
that this is a bug and that it should be fixed.  They said that if they get
enough complaints they _might_ fix it. 

It makes me wonder what other undocumented surprises reside in this machine.
This is ridiculous.


Christopher B. Moore
cmoore@space.mit.edu