Many years ago I learned how to do addition on a standard sliderule.
My engineering colleagues were always astonished when they were shown
this possibility as it is counter-intuitive. The basic sliderule
operation is to add logarithms. I have been wracking my brain trying
in vain to reconstruct the very simple process by which normal
addition can be performed on the standard sliderule. Does anyone out
there know how to to this?

Hello

there are many resources about sliderules on the web and I found it
quite overwhelming being that I have never used a sliderule myself.

But I found this on one of the sliderules newsgroups

"...I would like to mention again the only simple and easy
procedure that I know of performing sliderule addition (although I
never used it):

a + b = a (1 + b/a)"
(http://groups.yahoo.com/group/sliderule/message/4818)

Is this what you where remembering or looking for ?

Another newsgroup addressing sliderules addition issues is 
http://slashdot.org/articles/01/07/07/156226.shtml

I also found some interesting resources at
http://www.sliderules.clara.net/index.htm
and
http://www.sliderule.ca/

Hope this helps
silviares

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Request for Answer Clarification by hlf-ga on 14 Jul 2002 14:53 PDT

I could not find the comments icon! This is intended as a comment to
be helpful to others interested in the subject. The full process for
doing addition on the slide rule, thanks to the hint provided by
silviares, follows:

a + b = a (1 + b/a)

So we first perform the division operation by placing A on the C scale
over B on the D scale and reading the ratio (b/a). We mentally add 1
to the result and move the index ("1") of the C scale over the result
(1 + b/a). Then we look under  A on the C scale to find the result
[a(1+b/a)] immediately underneath on the D scale.

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Clarification of Answer by silviares-ga on 14 Jul 2002 16:25 PDT

Since hlf-ga couldn't find the comment icon and he posted his comment
as a request of clarification I have been called by Google Answers to
clarify.
There is not much that I can add. Thank you to hlf-ga for detailing
the addition process. As I said I have never used a sliderule myself
but I know enough math to see that it made sense and that hlf-ga would
have know exactly what to do.
I provided a couple of links of newsgroups in case the method was not
the one he remembers and in case he wanted to post the question to the
newsgroup himself.

The last two links in my answer were mostly to satisfy eventual
curiosity - and were pretty interesting to read and were rich in
pictures and documentation for old sliderules.

Thank you again,

silviares

The response was close to what I sought and was sufficient for me to
work out the rest by myself. Only the first link was helpful. I would
have preferred a complete solution, but this answer was sufficient
justify payment in full. I was very pleased by the speed with which
the answer was forthcoming. Previously I had tried "Ask Dr. Math"
without success. So, bravo for Google Answers and silviares-ga.
Additional comments would be welcome.

Howard