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November 2003

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From:
"Whittaker, Dewey (AZ75)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 5 Nov 2003 08:46:15 -0700
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Valerie,
Are you suggesting we launch a "counter" offensive to change that?
Dewey

> -----Original Message-----
> From: Valerie St.Cyr [SMTP:[log in to unmask]]
> Sent: Wednesday, November 05, 2003 8:38 AM
> To:   [log in to unmask]
> Subject:      Re: [TN] OFF-TOPIC: Engineering Specs :-)
>
>
> I believe (could be wrong) that standard PCB thicknesses of 1/16, 1/4,
> 3/32, 1/2  are what they are because that is what the thickness of counter
> top "laminates" were when the "laminators" started supply phenolic
> "laminates" to the fledgling PWB industry. Then connectors were designed
> to accommodate laminates of those thicknesses, and now we are stuck with
> standard thickness of .062", .093", .125" because those are the only (for
> the most part) thicknesses that "standard" connectors work with ....
>
> Valerie
>
>
> Valerie St. Cyr
> PCB Technology
> Teradyne
>
> 978-370-1136
> [log in to unmask]
>
>
>
>
>       Brian Ellis <[log in to unmask]>
> Sent by: TechNet <[log in to unmask]>
>
> 11/05/2003 10:13 AM
> Please respond to "TechNet E-Mail Forum."; Please respond to Brian Ellis
>
>         To:        [log in to unmask]
>         cc:
>         Subject:        Re: [TN] OFF-TOPIC: Engineering Specs :-)
>
>
>
> Of course, this makes the metric system look stupid. It makes much more
> sense to have 12 inches = 1 foot; 3 feet = 1 yard; 5.5 yards = 1 rod,
> pole or perch; 4 rods, poles or perches = 1 chain (the length of a
> cricket pitch between the wickets); 10 chains = 1 furlong; 8 furlongs =
> 1 statute mile. In summary, 1 mile = 8 furlongs = 80 chains = 320 rods,
> poles or perches = 1760 yards = 5280 feet = 63360 inches. It is this
> simplicity that dictates why printed circuits are largely dimensioned in
> imperial measures, rather than the complex metric system. Similarly,
> imperial weights, volumes, areas etc. are equally simple.
>
> Brian
>
> Ingemar Hernefjord (KC/EMW) wrote:
> > The history of length and weight is funny to read
> >
> > examples pasted from english history article:
> >
> > The foot was declared one-third yard and the inch one thirty-sixth. King
> Edward II in 1324 recognising the Iron Ulna was not universally used
> declared "3 barleycorns, round and dry make an inch"
> >
> >
> > Going as far back in time as Noah's ark, the lack of a universally
> understood unit of measurement was not a serious drawback. Most measuring
> was done by one craftsman completing one job at a time, rather than
> assembling a number of articles piecemeal to be put together later. It
> didn't make much difference how accurate the measuring sticks were or even
> how long they were. The cubit of Noah's time was the length of a man's
> forearm or the distance from the tip of the elbow to the end of his middle
> finger.
> >
> > For the United Kingdom, the basic English unit of length was the yard of
> three feet, or the fathom of six. Half a yard was the 18-inch cubit, and
> half a cubit was called a span, which was the distance across the hand
> from the tip of the thumb to the tip of the little finger when the fingers
> were spread out as far as possible. A hand was half a span. During the
> thirteenth century King Edward I decreed the 'Iron Ulna' after the bone of
> the forearm to become the main unit of measurement, which later became the
> 'yard'. He ordered a permanent measuring stick made of iron to serve as a
> master standard yardstick for his entire kingdom. King Edward realised
> that constancy and permanence were the key to any standard. The foot was
> declared one-third yard and the inch one thirty-sixth.
> >
> >
> > Regards
> >
> > Ingemar Hernefjord
> > Ericsson Microwave Systems
> >
> >
> >
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]]On Behalf Of Brian Ellis
> > Sent: den 4 november 2003 17:24
> > To: [log in to unmask]
> > Subject: [TN] OFF-TOPIC: Engineering Specs :-)
> >
> >
> > Origins of engineering specs
> >
> >   Subject:  Origins of engineering specs and government
> >   decisions. Ever wonder where engineering specifications come from?
> >
> >   The US standard railroad gauge (distance between the rails) is 4 feet,
> >   8.5 inches, an exceedingly odd number. Why was that gauge used?
> >   Because that's the way they built them in England, and the English
> >   built the first US railroads.
> >
> >   Why did the English build them like that?
> >
> >   Because the first rail lines were built by the people who built the
> >   pre-railroad tramways, and that is the gauge they used.
> >
> >   Why did they use that particular gauge then?
> >
> >   Because the people who built the tramways used the same jigs and tools
> >   that they used for building wagons, which used the same wheel spacing.
> >
> >   Okay! Why did the wagons have that particular odd wheel spacing?
> >
> >   Well, if they tried to use any other spacing, the wagon wheels would
> >   break on the old, long distance roads in England, because that's the
> >   spacing of the wheel ruts in the granite sets.
> >
> >   So, who built those old rutted roads?
> >
> >   Imperial Rome built the first long distance roads in Europe (and
> >   England) for their legions. The roads have been used ever since.
> >
> >   And the ruts in the roads?
> >
> >   Roman war chariots formed the initial ruts, which everyone else had to
> >   match for fear of destroying their wagon wheels. Since the chariots
> >   were made for (or by) Imperial Rome, they all had the same wheel
> spacing.
> >
> >   The United States standard railroad gauge of 4 feet, 8.5 inches is
> >   derived from the specification for an Imperial Roman war chariot.
> >
> >   Specifications and Bureaucracies live forever.
> >
> >   The Imperial Roman war chariots were made just wide enough to
> >   accommodate the back ends of two war-horses.
> >
> >   Now let's cut to the present...
> >
> >   The Space Shuttle, sitting on its launch pad, has two booster rockets
> >   attached to the sides of the main fuel tank. These are solid rocket
> >   boosters, or SRBs. A company builds SRBs at its factory in Utah. The
> >   engineers who designed the SRBs wanted to make them a bit fatter, but
> >   the SRBs had to be shipped by train from the factory to the launch
> site.
> >
> >   The railroad line from the factory has to run through a tunnel in the
> >   mountains.
> >
> >   The SRBs had to fit through that tunnel, which is slightly wider than
> >   the railroad track, and the railroad track is about as wide as two
> > horses'
> >   behinds.
> >
> >   So.... a major design feature of what is arguably the world's most
> >   advanced transportation system was determined two thousand years ago
> >   by a horse's ass.
> >
> >   Which is pretty much how most government decisions are made.
> >
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