Subject: Re: metric vs. inches

From: [email-masked] (Chris Pollard)
Date: 21 Sep 1996 05:59:36 GMT

[email-masked] wrote:

:    Finally, most people don't call it the "American" measurement system;
: we call it "English" because the Brits inflicted it upon the unsuspecting
: colonies before abandoning it themselves.  We should be angry.   It gets 
: worse than 3's and 12's.  Acres are squares of something like 216 feet on
: a side, and old deeds use rods (or poles) as units of measurement, and old 
: maps sometimes even use leagues (whatever that is).  A lot of our old 
: land records are incomprehensible.  
You will very pleased to learn then that the standard metric pipe thread
is BSP (British Standard Pipe) and it actually isn't a round number of
inches or  mm.

---

From: "Tony P." <[email-masked]>
Date: Sat, 21 Sep 1996 05:14:19 -0700

Not really surprised.   Somebody mentioned that the "only thing not 
metric" on many U.S. cars is the sparkplugs.  They would be surprised to 
remember that sparkplugs were the _first_ thing on U.S. cars to use 
metric measures.  The old 15 mm vs 18 mm plugs have been around for forty 
years.

   Funny thing is that, while the diameter of the hole is metric, the 
thread on the plug is not.  Actually, the great difference in metric 
standard threads is more of an impediment to the switch than the fiddling 
around and squawking we do.

---

From: [email-masked] (Steve Rayner)
Date: Sun, 22 Sep 1996 09:41:47 GMT

Has anyone tried sorting 11mm & 12mm nuts?

In a previous article, [email-masked] ("Tony P.") says:

>idt.net!news
>From: "Tony P." <[email-masked]>
>Newsgroups: rec.crafts.metalworking
>Subject: Re: metric vs. inches
>Date: Sat, 21 Sep 1996 05:14:19 -0700
>Organization: Very, very poor.
>Lines: 10
>Message-ID: <[email-masked]>
>References: <[email-masked]> <[email-masked]>
>NNTP-Posting-Host: wpb-134.magg.net
>Mime-Version: 1.0
>Content-Type: text/plain; charset=us-ascii
>Content-Transfer-Encoding: 7bit
>X-Mailer: Mozilla 2.01 (Win16; I)
>To: Chris Pollard <[email-masked]>
>

-- 
Steve.

**************  BE ALERT, THE WORLD NEEDS MORE LERTS ************************

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From: [email-masked] (PnP Nolan)
Date: 22 Sep 1996 12:20:53 -0400

In article <[email-masked]>, [email-masked] (Chris Pollard)

>is BSP (British Standard Pipe) and it actually isn't a round number of
You might also check out ACME threads for a Metric counterpart. <g>

---

From: <[email-masked]>
Date: 21 Sep 1996 03:45:59 GMT

I don't think it's as complicated as you believe.  The confusion comes
in distinguishing between the way we calculate and the way we subjectively
think and visualize.

   We grow up identifying objects in inches, and for life, we visually
estimate linear distance in inches, feet, yards, etc.  We are kind of stuck
with that, and as adults mostly have to estimate in those units and
mentally convert to metric if necessary.  Most people just never
develop an "eye" for metric dimensions (in my generation, anyway).

    On the other hand, calculating is much simpler than it sounds.  The rulers
we use are marked in half, quarter, eighth, sixteenth and 1/32 units.  Nobody 
uses, say 12ths of an inch.  The math gets complicated when adding, since
you must add feet, inches, half, quarter, eighth inches, etc, then reduce as 
far as possible (say 11/16ths or 7/8ths or 17/32s, but not 12/16ths [3/4] or 
16/32 [1/2].

   Anyone dealing with measurements daily ignores yards.  100 yards is 
just 300 feet.  Also, any professional uses decimals, and we all learn early to
do so as well in any precise work.  Thus, a surveyor would say 127.83 _feet_
and ignore yards and inches, or a technician may say 43.87 inches and 
ignore feet.

   The trick is converting the eighths, 16ths, etc into decimals, which
we all do mentally, sometimes badly, and a lot of errors result.  I have a
mental block about 16ths and check my answer twice.

    Since we all learn early to use decimals anyway, the switch
to metric is simple, but we adults can't get comfortable with the units.
I'll never visualize a millimeter or centimeter accurately without thinking
in inches first, and a meter is easier only because it's a bit more than a yard.

    Trying to switch the other way (from metric)would no doubt be a 
nightmare, but it's not quite as bad as you suspected.   If you can 
deal with inches and feet, and handle eighths and sixteenths, you're all set.  
Ignore the yards.  In fact, ignore the fractions and stick to decimals 
(e.g. 3.35 in. or even 3.65 feet) and you'll usually be fine.  Any engineer 
or technician you deal with is doing the same anyway.

   Finally, most people don't call it the "American" measurement system;
we call it "English" because the Brits inflicted it upon the unsuspecting
colonies before abandoning it themselves.  We should be angry.   It gets 
worse than 3's and 12's.  Acres are squares of something like 216 feet on
a side, and old deeds use rods (or poles) as units of measurement, and old 
maps sometimes even use leagues (whatever that is).  A lot of our old 
land records are incomprehensible.  

    They did the same thing with their money (shillings and guineas and crowns 
and what-all) and calendars (what's a fortnight?).  Pounds are 16 ounces, 
Were they also 16 shillings?   An ounce is 1/16th of a pound (mass 
measurement), but it's also 1/16th of a pint.  A pint isn't a pound unless
the bottle is full of water (one fluid ounce of water = one ounce weight).
Why is a gallon 128 ounces? And why isn't an Imperial gallon the same as 
a normal gallon?

    Why are there Troy ounces and avoirdupois (?) ounces? 
Why do we have drams and grains?  Fathoms?  Why is a Ton 2000 pounds?
(because it's a hundred stone?)

   None of it makes sense, but I have $10,000 worth of tools in inches
and when I have to work on metric fasteners, it takes me four tries
to grab the right metric wrench, so I hope I'm long gone when we finally 
switch over completely.

    One question for you:  a millimeter is tiny, and a centimeter is very small.  
A meter is very large.  You need something in between.  Do you
use decimeters?  Probably not, I guess.

---

From: "w.j.ward" <[email-masked]>
Date: 24 Sep 1996 02:05:27 GMT

PnP Nolan <[email-masked]> wrote in article
<[email-masked]>...
> You might also check out ACME threads for a Metric counterpart. <g>

As an engineer, I have suffered through several years worth of applied math
classes where we used both English and metric units.  In the days before
the hand-held "scientific" calculator (days I'm glad to say I don't
remember), the metric system really made sense.  Now, with calculators that
will do the conversions for you, I don't really think it matters very much
which system is used.  I've used both systems.

One thing I would like to point out, though, is that when it comes to
computers, they "think" in powers of 2, not 10.  So, what would be easier
for a computer to handle, 64ths of an inch or 1000ths of a meter?

-- 
(Remember..if it doesn't work,  Microsoft doesn't care.
And Compaq charges $35 to ask "why?".)
W.J.Ward

---

From: [email-masked] (Kevin AstirCS "1U" KO0B)
Date: Tue, 24 Sep 1996 18:52:39 -0700 (PDT)

A little off topic, but my dad (who, AFAIK never touched a computer)
loved to hear how they applied to his "real world".

>for a computer to handle, 64ths of an inch or 1000ths of a meter?

Good point.  In base 2, rational decimal fractions (.1 is an example)
are irrational (require infinite digits to represent exactly), as 1/7
and 1/3 are in decimal. ( which are just  .1 in base 7 or  3)  (I know
some machinists, who really should be using base 7 or 8 ;-)

In computerized controls (my background in flight controls, but
matters for CNC also) it is important to keep error due to rounding
(keeping only "n" digits) from accumulating (read that as "drift")
over time or repeated motions.  To that end, everytnig is normalized
to units exactly representable in base-2, giving a so-called fixed
point system...in the end you may round off and tell the 10 fingered
pilot 10.6 degrees flap, but the computer is actually maintaining 10
5/8 degrees. (which it knows only as 85 arbitrary units)

Now on a CNC machine, you just make the steps equal to a tenth (or
half a tenth), and then you're computer need only deal in whole
numbers of steps (it has no problem using really big numbers!) .....In
the above example, each unit represents 1/8 of a degree,...so the
answer is the computer doesn't have to deal with fractions OR
decimals, and it could care diddly about what the "real" units are.
But don't go measuring angles with radians.. .you need to break a
circle into some integer number of units, unless you really _don't_
want to index from one turn to the next..  

Because programmers who can deal with such "arbitrary units" demand
higher salerys than those who can't, there is some effort to improve
so called "floating point" control systems.  They tend, however, to
display hard to track down bugs, and non-repeatable errors.  The
techno-buzzword is "non-deterministic". The true location of the
cutter might depend heavily on the path by which it came if such a
controller were running a CNC machine...not what you want.

-KF-

---

From: Janos ERO <[email-masked]>
Date: Wed, 25 Sep 1996 14:12:42 GMT

> in distinguishing between the way we calculate and the way we subjectively

Thank you for this posting. It was a pleasure to read.

> Most people just never

> in inches first, and a meter is easier only because it's a bit more than a yard.

If you really want to get more familiar with metric sizes, I suggest you to have a 
metric ruler. Or perhaps a caliper.

> or technician you deal with is doing the same anyway.

Yes we do. In the electronics all sizes were until the recent times all inch. All 
integrated circuit and connector pinouts, board layouts etc. A REAL nightmare was 
when I encountered in the '80s East German ICs where the pinout was 2.5mm instead of 
.1" (2.54mm). First you don't recognize the difference, but at a 40 pin IC the 
difference grow up to .76mm, 0.03 inch. Big enough not to fit into the socket!

> (because it's a hundred stone?)

The biggest problems for me are the pressure units. Even the metric system uses two 
of them: Pascal, which is Newton per square meter, a very small unit. Even if you 
blow out a candle, you pressurize the air to several Pascals. More common is the 
Bar, which is 100000 Pascal. This is really very close to the atmospheric pressure, 
thus a quite handy unit. But it is not compatible with the kilo-, mega- etc. system, 
as it is 100 kilopascal, or 0.1 Megapascal ! Hard to compare however with psi 
anyway.

Another complicated calculation is if a metric guy speaks about the fuel consumption 
of his car as liters for 100 kilometers. Try to change this to miles per gallons. 
And there are two gallons :-)

BTW even the most continental (:-)) countries use some rests of the inch system. In 
most countries the bike wheel size is given in inches, and the gas and water tubing 
uses both inch size tubes and threads (Witworth). 

> to grab the right metric wrench, so I hope I'm long gone when we finally

Just a rule of thumb (not always true): the standard wrench size is apr. 1.6x thread 
size: M3 - 5.5mm (the only half mm!), M4 - 7mm, M5 - 8mm, M6 - 10mm, M8 - 13mm. 
Unfortunately this is not true for bikes, I don't know why, and for some Japanese 
cars.

> use decimeters?  Probably not, I guess.

Forget about please. The first thing we learnt on the Technical University was: 

"In the metalworking and similar industry we ONLY use millimeters !!!"
----------------------------------------------------------------------

(Centimeter is something for taylors, architects and carpenters.)

I have copies of several steam engines from the last century. Even their length is 
given in millimeters !!! (like 17,876mm)

---

From: "Tony P." <[email-masked]>
Date: Wed, 25 Sep 1996 21:52:56 -0700

Whew!  That's quite an explanation.  I thought I was computer 
literate, and have three university degrees, and barely followed it.  
Lots of thought went into it, obviously.

   I think though that whether computers are digital or decimal or 
whatever) they will have _very_ little difficulty dealing with the 
metalworker's or carpenter's conversions and calculations, whatever 
system he's using.

   I understand your argument about "drift" and rounding error: very good 
points when calculations are made in series without repeated reference to 
a point of beginning or reference, as your control systems must 
apparently do.  Surveyors get in lots of trouble that way, and if you've 
seen the old government survey-lines, it's obvious.

   That, BTW, is the thing I will never understand about inertial 
navigation systems:  without repeated references to a centering or 
cross-reference point, don't the tiny errors (such as rounding, but 
measurement too) add up to gibberish after a few hundred miles?  Our 
machines are a whole lot smarter than I can grasp.

  (Of course, I still can't manage to grasp the control system of a fast 
printer head or, for that matter, a hard drive, for many of the same 
reasons.)

					Tony

---

From: "Tony P." <[email-masked]>
Date: Wed, 25 Sep 1996 22:11:02 -0700

Thanks for your kind comment ([email-masked] is also 
[email-masked].  Two 'Net providers so I never get a busy 
carrier)

    I really enjoyed your thoughtful response.  The world has now shrunk 
to the point where everything our neighbors do is relevant.  A distance 
of thousands of miles is no distance at all, but a cultural gulf can be 
insurmountable; fortunately there are only a few of those left, mostly 
involving religion.

   Anyway, it's a lot of fun looking over the shoulder of skilled and 
thoughtful people working in different ways and systems.  Invariably, I'm 
struck more with how similarly we end up doing things than the reverse.  
Things always seem a lot more "different" in the abstract than in 
practice by other humans.

   Now I just need to learn to recognize those metric fasteners according 
to the chart, rather than just grabbing wrenches by eyeball.  I'm afraid 
I'm doomed to a lifetime of grabbing a metric nut and trying to turn it 
onto an inch bolt.  _Very_ frustrating, because there are no two 
different inch-sized nuts close enough to be mistaken for each other that 
way, but the doggone metric things just _look_ the right size and I'll 
grab them every time.  Once I get them into my nut and bolt bins it's 
like a case of fleas that can't be gotten rid of.

	Just another challenge.

					Tony

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From: [email-masked] (Russ Kepler)
Date: Thu, 26 Sep 1996 15:37:11 GMT

>machines are a whole lot smarter than I can grasp.

Not if the errors cluster about the zero point - then they average
into nothing but dither over time.

-- 
Russ Kepler							[email-masked]

                    Please Don't Feed the Engineers

---

From: [email-masked] (Kevin AstirCS "1U" KO0B)
Date: Thu, 26 Sep 1996 15:52:11 -0700 (PDT)

My previous post contained an error, pointed out in private e-mail by
an australian gentleman. *

Irrational numbers are those that can't be expressed as a fraction of
whole numbers. (literaly "not a ratio") pi is irrational, 1/3 is not,
even though 1/3 can't be expressed _exactly_  in decimal form without
infinite digits.....Neither I nor the corrispondant know the correct
word for that.

Tony posted:

>measurement too) add up to gibberish after a few hundred miles? 

Yup, but the drift in modern laser gyros has been reduced to the point
where INU's are quite usable for several hours at jet speeds .  They
are also tied into flux gate compasses, and nowadays GPS system .  GPS
gives absolute position as basic output, so positional errors don't I
accumulate.

I admire the way this group stays on topic, which isn't what this
branch of the thread is doing....so if anybody wants to persue the
topic further, please contact me my private e-mail, and appologies to
those who have suffered this far.

*turns out I know his brother in Vienna Austria..net is sure shinking
the world!