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The slide rule was used everywhere, not just the moon landing.  Consider, the 
electronic 4 function (+-*/) calculator was marketed the early 1970's.  I 
still fondly recall my first calculator and marveled at the decimal digits 
and the speed.  I wouldn't let anyone touch my precious instrument!  Any 
engineering that was done before 1973 either used a mainframe computer or a 
slide rule.

Mainframe computers were gigantic beasts.  Nothing like the desktops of today 
at all.  Remote operations happened (at least for me) at 110 baud.  Yawningly 
slow.  Even when you were local to the mainframe, things took time.  You 
submitted a job and the answer, after a period of time, popped out.  They 
were expensive to operate and maintain.  Associated with the mainframe was a 
staff. Your job was scheduled in, there was no instantaneous gratification.

The slide rule offers immediate results, with an answer that almost always is 
"good enough".  The 10" rules were like a sword on your belt.  Very awkward 
to wear.  I still have my pocket slide rule which did not suffer from that, 
at the expense of even further resolution issues.  I kept the 10" at my desk 
and the small one in my pocket.  The small one popped out in meetings.

The slide rule offers something that all the electronics in the world does 
not.  It is the Order of Magnitude of the problem.  That is, you are forced 
to estimate the answer in your head first and then stick the decimal point 
where it belongs.  Essentially, you solve the problem before hand and the 
only thing the slide rule does is to refine the decimal digits of accuracy.  
Since you only have 2 or 3 digits after the decimal point (typically), you 
are forced to be conservative in your calculations.  That's why many 
structures that were created with slide rules appear to be "solidly 
constructed". They were compensating for the inability to resolve the 
problem.

I don't want to discourage you, yet I believe that the solution to the 
spherical triangle on a 10" slide rule will not be of sufficient accuracy to 
suit for navigation.  There simply isn't enough resolution.  Dutton 
recommends that each navigator equip himself with one, but I believe that 
this is to perform simple rate equations and trigonometric solutions, not for 
the solution of a spherical triangle.

Mind, you will get a solution.  That solution will put you on the map.  The 
only thing is just how accurate your answer is and how much do you need!

Best Regards
Brad





-----Original Message-----
From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Greg Rudzinski
Sent: Wednesday, May 20, 2009 12:50 AM
To: NavList
Subject: [NavList 8330] Re: recommendation for slide rule ?


Gary,

     You have succeeded in getting me interested in slide rules. I
have never owned or used one but after some internet research I see
that they have been to the moon and back. Now I will have to get one!
So far I am leaning toward the purchase of a Pickett N3-ES which is of
aluminum construction. The slide rule could very well be the pinnacle
of low tech achievement. Right there with the mechanical chronometer.

Greg

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