The Risks Digest

The RISKS Digest

Forum on Risks to the Public in Computers and Related Systems

ACM Committee on Computers and Public Policy, Peter G. Neumann, moderator

Volume 4 Issue 68

Thursday, 26 March 1987


o Re: Health hazards associated with VDU use: eyestrain
Barry Gold
o ... and fluorescents (Re: RISKS-4.67)
Brad Davis
o ... and related injuries
Jeremy Grodberg
o Conference on Computers and Law
David G. Cantor
o Re: runaway motors
Don Lindsay
o The social implications of inadvertent broadcasts
Donn Seeley
o Re: Increased Telephone Switching Capabilities
Andrew Klossner
o Re: phone number of caller
Don Lindsay
Jeremy Grodberg
o Hang-ups
Paul Wilcox-Baker
o Info on RISKS (comp.risks)

Re: Health hazards associated with VDU use: eyestrain

Barry Gold <lcc.barry@CS.UCLA.EDU>
Wed, 25 Mar 87 17:13:43 PST
PGN's comment on the light spectrum from fluorescents ignored another
"feature" of fluorescents: stroboscopic distortion.  Take a small, bright
object (like a pencil) and wave it back and forth under sunlight or
incandescent light; you'll see a blur.  Do that under flourescents and
you'll see several copies of the object.  Get the frequency right and you
can even read the lettering on the pencil.

This means that movements (including the ones caused by your constant
eye motion) that would normally be smooth blurs (no feature to attract
your auto-focus mechanism) work in jumps that can cause your eye muscles
to try to track them.

An earlier posting on VDUs suggested keeping them at or above eye level.
There is another good reason (besides neck strain) to do this.  Our
eyes were evolved for light coming from above.  You'll notice your
upper eyelashes are longer and thicker than the lower.  And if you shave
off your eyebrows and spend much time outdoors, you'll suffer eye damage
(bet you thought eyebrows didn't have any function).

I keep my crt on an empty IBM PC box.  This puts the bottom of the screen
about level with my eyes.  And most of the light--both from the screen
phosphors and room light reflected off the screen--comes from above, as
it should.  I seem to be able to work more comfortably this way.

                                  [Me too.  Excellent advice.  Thanks.  PGN]

Risks of Displays and Fluorescents (Re: RISKS-4.67)

Brad Davis <b-davis@utah-cai>
Wed, 25 Mar 87 14:15:40 mst
[...] Or the 60 hz beat.  I personally keep the window blinds open as long
as possible since sunlight is better for stress and depression than most
(read 'our') artificial lights. 

Brad Davis  {ihnp4, decvax, seismo}!!!b-davis

About CRT related injuries:

jeremy grodberg <rochester!kodak!grodberg@seismo.CSS.GOV>
26 Mar 87 22:23:44 GMT
   Since I started working as a professional computer programmer, my
eyesight has deteriorated from better than 20/20 to 20/60, with the bulk of
that change (20/20 to 20/40 coming in the first 4 months).  I have seen 3
different opthomologists who all agree my eysight degradation is due to
excessive reading, but have been unable to stop the decay with glasses,
excercise or drugs.  I have now been at it 2 summers + 1 year since the
first problems, and have little hope of reversing the damage even if I give
up reading all together.  While this injury is not necessarily related to
CRT's, it is indicative of injuries that are occupational hazards with
little hope of avoidance.  My choice was to either lose (to some extent) my
eyesight or switch to another profession.  Until I am able to support myself
some other way, I pretty much have to sacrifice my eyesight.
                                                              Jeremy Grodberg

Usenet: ...rochester!kodak!grodberg

Conference on Computers and Law

David G. Cantor <dgc@CS.UCLA.EDU>
Wed, 25 Mar 87 20:55:59 PST
       A Technologist's Guide Through Legal Pitfalls and Pathways
        October 21-23, 1987 at Santa Monica, California

Sponsors:  IFIP Technical Committee On Computers and Society and
       Los Angeles County Bar Association Law and Technology Section


Technology, law or the professional?

Technical and policy professionals are being forced to confront a maze
of nascent legal realities and threats.  These span private contracts,
tort liability, the public interest, iminal prosecution, and myriad
other issues and relationships, and encompass the regulation and
protection of technology and data as derived from economic and political
rights.  Yet many problems are ill-defined and solutions are not widely


To bring together computer and information professionals who must make
technology-based decisions and lawyers who are faced with representing
their interests in order to identify common problems, to explore the
dimensions of their alternatives, and to understand the consequences of
their responses.


Taxation and computing
Protection of intellectual property rights
Information-system imes and defenses
Legislative policy and technical issues
Telecommuting and independent contracting
Export-Import controls
Computer security---fact and fiction
Civil vs. criminal remedies: Victim options
Computer policy in developing nations
Government information policies
Database abuse: Public responsibility and private gain
Recognizing and minimizing exposure for product and service liability
International contracting for hardware, software, and computer services
Malpractice potential: Computer delivery of professional services
Resolving computer-contract disputes: Techniques and standards
Emerging technologies:  Enyption, artificial intelligence, networks, and
    other problem areas
Public (dis-)service: Automating the criminal justice system
Independent verification and validation of computer generated information

    Papers should strive to report important experiences and to identify
    key, open areas.  We encourage tutorials for non-specialists, and
    presentations supported by check-lists and procedural guides.  We
    also solicit panel-discussion proposals.  Provocative comment is


Original papers of up to 5000 words (20 double-spaced pages) are
invited on the above and related topics.  Papers which highlight actual
user experiences, with specific legal entanglements or solutions, are
preferred over abstract explorations.  Papers will be refereed and
accepted papers will be published in the Conference Proceedings.  Format
instructions for camera-ready copy will be provided when the paper is
accepted.  Please send FOUR copies of the paper, including a 300-500
word abstract, to the CONFERENCE CHAIR, Michael M. Krieger, P.O. Box 24619, 
Los Angeles, CA 90024, 213-394-4356, Internet:


Papers due: May 6, 1987 Acceptance: June 5, 1987 Final copy due: July 15, 1987

ORGANIZING COMMITTEE: Jay BloomBecker, Los Angeles (program chair),
Richard Bernacchi, Los Angeles    David G. Cantor, Malibu
Steve ocker, Los Angeles          Eric Delissy, Geneva
Charles Firestone, Los Angeles    Jochen Haber, Los Angeles
John Helly, Los Angeles           Richard Horning, San Franscisco
Leonard Kleinrock, Los Angeles    Dr. Wolfgang Kilian, Hanover
John Lautsch, Anaheim             Ira D. Moskatel, Beverly Hills
T. R. H. Sizer, Farborough        Dr. Artur Solarz, Stockholm
Wilhelm Steinmuller, Bremen       Alan S. Wernick, Columbus
David C. Tunick, Los Angeles (proceedings editor)

Re: runaway motors [and a fish tale?]

Wed 25 Mar 87 10:58:44-EST
Theatrical riggers are not the only people in the world with computer-
controlled motors. 

Some friends of mine set a good example when they retrofitted computer
controls onto a mechanical stereo-interpreter. This machine is used to make
topographical maps from aerial photographs ("stereo pairs", hence,

The machine had a mechanical stage, with arms driven by ultra-precise worm 
gears. The stage had mechanical stops - that is, solid objects which the arms
would have to run into before leaping onto the floor. My friends changed the
drive, of course, and the resulting machine was quite fast. I recall seeing
the arms travel six feet in under a second. (This includes decelerating
to a stop.)

The machine acquired several layers of computer equipment. At the low level,
there was a microprocessor per motor, and detection hardware so that precision
could be obtained by feedback. At the higher level, of course, one made maps.

The design incorporated simple limit switches. These switches tripped
when the arms got out of bounds, and shut off the power to the motors.
The basic idea was to keep the arms from hitting the mechanical stops at
high speed. This would prevent damage to the arms, and also, would prevent
then from bouncing over the stops and onto the floor.

The wise thing that my friends did, was to install the limit switches FIRST.
The computer interface to the limit switches was added LAST.

In the course of the project, it was noticed that there was a single major
failure mode. The arms would go past the limit switches at maximum 
acceleration. This was the result of practically anything - timing glitches,
byte-ordering bugs between machines, reading a device register while it was
rippling, you name it. 

I heard a related story from a friend working on irradiation therapy machines.
He reported that an older machine of theirs was once involved in an tragedy.
Reportedly, a patient had been killed because the hydraulics ran away, and
crushed the patient against the radiation shielding. The operator had hit the
emergency-off switch, AND IT DIDN'T WORK. The switch removed power from most
of the machine - but not from the hydraulics.

And then, there is the story that I heard about a real-time programmer who
was computerizing a fish-filleting factory. As I heard it, a side effect of
debugging was that he got to feed every stray cat in Stockholm ...

Don Lindsay
                    [This is known as REEL-TIME Programming.  Must have 
                    been "Salmon-Chanted Evening" for the cats.  PGN]

the social implications of inadvertent broadcasts

Donn Seeley <>
Thu, 26 Mar 87 02:31:36 MST
                       [This is somewhat marginally relevant, but 
                       it seemed worth including anyway.  PGN]

I happened upon this in the New York Times (3/21/87, p. 12).  '... [I]n
February, The China Daily reported this week, ... a woman trying to
copy an obscene film called "Massage Girl" at a television station
inadvertently broadcast 20 minutes of the movie to homes throughout
Guangdong Province.  The woman was arrested.'

I live in a state where the attorney general's office has spent
$600,000 in public funds to appeal a ruling that the legislature's
cable TV censorship law is unconstitutional, and where a local
newspaper that has recently stopped printing the controversial comic
strip Doonesbury is now debating whether to continue to buy the strip
and not publish it so that the population at large need not suffer from
its presence.  An 'inadvertent broadcast' like the one described above
could have a serious impact on civil liberties here, especially if it
occurred on a cable channel.

Donn Seeley    University of Utah CS Dept

Re: Increased Telephone Switching Capabilities

Andrew Klossner <>
Wed, 25 Mar 87 15:08:58 PST
This topic was discussed at length in the TELECOM list.  Some items ...

    "I discussed this article with a friend, who [asserted that]
    the information (calling #) is already available, and is
    encoded somehow just prior to the ring spike on the receiving

There is no truth to this statement.  Under normal circumstances, when
the originating and receiving exchanges (CO's) are different, the
receiving exchange has no way of knowing the origination number.

    "I don't see any obvious risks to the new features."

On of my concerns is that, with these features, I can no longer keep my
unlisted phone number private.  If I call a local department store to
get their price on a pair of shoes, I may start getting unsolicited
shoe sales calls from all over.  Merchants would be motivated to
collect and sell lists of phone numbers of consumers with particular
interests, just as they now collect and sell mailing addresses.  (And I
can't make use of that "call screening" feature; what if my daughter is
in trouble and tries to call home from a phone booth?)

MORE:  Re: Michael Wagner (RISKS-4.67)

  "1) the 911 emergency number in Toronto displays the number
  from which a call was made...

An originating exchange sends the information only when it's using the
special 911 subsystem.  (At my exchange this goes out on a special
trunk directly to the 911 center, it doesn't travel between exchanges.)
The implications don't follow.

  "2) The University of Toronto recently switched over to a Centrex III
  system.  Certain (secretarial) phones can now display the number called and
  the number calling.  The number calling works only if the call originated
  within the centrex exchange.  It is not clear whether the restriction is
  technical or legal...

It's technical, that's the Centrex system talking to itself.

  -=- Andrew Klossner   (decvax!tektronix!tekecs!andrew)       [UUCP]
                        (tekecs!andrew.tektronix@csnet-relay)  [ARPA]

Re: phone number of caller

Wed 25 Mar 87 11:19:30-EST
At first glance, it seems simple to be told where your caller is calling from.
All that one needs is a small display: after all, exchanges are computerized
now, aren't they ?

Well, yes, new ones are. Also, new exchanges tend to be bigger: several
exchange numbers are implemented by a single office, rather than being
one-for-one. And, of course, if all the action occurs within a single
exchange, then the features that are offered are just a Small Matter Of

However, old phone exchanges are still with us. Projected reliability
used to be stated as outage-time per forty years !  Also, old designs
were being built until recently. For example, Bermuda bought a mechanical
stepping exchange (from Philips) in the early 1970's.

When authorities try to trace phone calls, the major stumbling block is
usually that the call has crossed one or more boundaries between exchanges.
Tracing then becomes a serial process, and it used to involve a human
at each physical location. A person wishing to (say) utter death threats
was quite difficult to catch, particularly if rural equipment was in the

Of course, we will eventually resolve these problems. Mad bombers will
respond by using pay phones, unattended autodialers, and other tactics.

Don Lindsay

Who called? (Re: RISKS DIGEST 4.66 and 4.67)

jeremy grodberg <rochester!kodak!grodberg@seismo.CSS.GOV>
26 Mar 87 22:58:37 GMT
    According to _High Technology_, a caller placing a call from an unlisted
phone can prevent the number from being displayed on the destination phone
by entering a code.  The phone company equipment still gets the number
though, so the person being called can call still call the person with the
unlisted phone number (using a feature which dials the number of the most
recent incoming call), although there is no (legitimate) way to actually
determine the unlisted number.
                                      Jeremy Grodberg

Hang-ups [Re: RISKS-4.67]

Paul Wilcox-Baker <dual!paul@ucbvax.Berkeley.EDU>
Wed, 25 Mar 87 09:24:37 pst
  > As far as I know it depends on the "office" (telephone company term for 
  > switching equipment) connected to your phone...  An electronic office will
  > close the connection as soon as either party hangs up.

Actually, this is not true.  For most electronic exchanges in the U.S., the
connection is held until about 20 seconds after the called party hangs up, or
whenever the calling party hangs up.  This is supposed to let the answering 
party hang up one phone, move to a different room and continue using another.  
The timeout is reset every time the phone goes off-hook.  This causes the
apparent inability to get rid of the incoming call.  The best solution to
obnoxious electronic calling machines is legal - ban the damn things!

Paul Wilcox-Baker.

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