# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Geeks [slide] rule!
From: Lu Abel
Date: 2013 Mar 28, 12:16 -0700
Two comments on the Brooklyn Bridge:

1.  It was designed to carry subway and street car traffic and did so until WW II.  Comparable loads to the yet-to-be-invented automobile when it opened in 1883.  If you go to the Wikipedia article on the bridge, it includes an 1899 Edison movie of electric subway cars and horse drawn wagons crossing the bridge.

2.  One of the biggest problems in building the bridge was not its design but in obtaining steel suspension cables that met the (reasonable) specifications for cable strength.  (Subcontracts for the bridge, including its cables, were being steered by political bribes, not quality of product.)  This actually caused the Roeblings (father and son) who built the bridge to form their own steel company, Roebling Steel, which operated until 1980.

To: luabel{at}ymail.com
Sent: Wednesday, March 27, 2013 5:32 PM
Subject: [NavList] Re: Geeks [slide] rule!

Hi Alan
Using a slide rule teaches you the magnitude of the answer.  You must already have an idea of the order of magnitude of the solution so you know where to put the decimal point.
When designing with a slide rule, you put in safety margins and never ever try to engineer something to within an inch of its life.  And, surprise, the Brooklyn Bridge still carries heavy traffic everyday, yet it was designed before the automobile was invented.
The beauty of the slide rule is that precision is related to length.  Hence the Bygrave can solve the celestial triangle to an arc-minute.  If you want more resolution, just make the scale longer.   Bygrave wrapped his scale around a cylinder.  So did Otis King and the Fuller by Stanley.
And to think it all started with Napier, but became popular because of navigators(!), using a Gunter's rule.
On Mar 27, 2013 8:12 PM, "Alan S" <alan202---net> wrote:

Sean, Brad and anyone else interested re slide rules, with which I'm NOT especially handy, never having much used them, still:
1. There are whole lot of old buildings, bridges, that sort of things, the design calculations for which were done with slide rules. The above mentioned are still in use.
2. Slide rules will not produce 5 decimal accuracy, assuming that such are desired or needed. Where a couple, perhaps 3 decimal places will serve, slide rules will also, and they are sometimes faster than calculators.
3. With slide rules, if the answer looks really wacky, it likely is.
4. One can scratch their heads with one too, no batteries required.
Alan
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