[sdiy] Metric vs imperial, was: My new Moog 960 sequencer clone module project.. slowly but surely ..

[David G Dixon]

Well, as someone who moved from an Imperial country (USA) to a metric
country (Canada), I can tell you that the transition is actually pretty
easy.  One starts to think in kilometers pretty quickly for driving.
Celsius for conveying the ambient temperature takes a bit longer, because to
an American, 30 degrees is just freaking cold, and to a Canadian, 100
degrees is for boiling water.  However, eventually even an old American can
learn to appreciate a 6-km walk in sunny 20-degree weather.

For engineering, many people don't realize that there are actually three
different metric systems, and this causes problems.  There is the archaic
and largely obsolete "cgs" system, where the basic units are centimeters,
grams, and seconds.  This gives rise to some very tiny units which are
utterly useless for engineering work, such as the dyne of force and the erg
of energy.

Then, there is the "mks" system which is mostly what is used today, with the
basic units or meters, kilograms, and seconds.  This gives rise to all of
our standard units: Newtons of force, Joules of energy, Watts of power,
Pascals of pressure (which are still too small, so we have the "bar" which
is 100000 Pa, and which is about 99% of a standard atmosphere), etc.

However, there is a third system, the so-called Systeme Internationale or SI
system.  Most engineers think (wrongly) that this is just the mks system,
and it "mostly" is.  However, for those in the chemical sciences, we have
inherited some very stupid conventions from chemists, who have made the
"standard" unit for moles the gram rather than the kilogram.  This means
that the "gram-mole" (which is a cgs unit) is mixed with other mks units in
some important and well-used constants, such as the Gas Constant R --> 8.314
J/gmol/K, or 8.314 Pa-m^3/gmol/K.  Of course, this should actually be 8314
J/kmol/K, using the kg-mole rather than the g-mole to keep it all in mks
units.  I tried at one point to make this change with my students, but it
didn't stick.  So, even with metric, we chemical engineers end up with
factors of 1000 all over the place, and many many many many many mistakes
are made because of this rank stupidity.  Given the situation with units,
it's really a miracle that anything works at all.

 

-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Tom
Ivar Helbekkmo via Synth-diy
Sent: Wednesday, November 11, 2020 5:11 AM
To: Donald Tillman
Cc: synth-diy at synth-diy.org
Subject: Re: [sdiy] Metric vs imperial, was: My new Moog 960 sequencer clone
module project.. slowly but surely ..

[CAUTION: Non-UBC Email]

Donald Tillman <don at till.com> writes:

> Of course I recognize and appreciate the advantages of the metric 
> system.  It's great for scientific work.  But for everything else; 
> engineering, design, culture, regular life... the metric system 
> becomes a serious disadvantage.

It depends.  You mention engineering.  Talk to a machinist, working in the
United States, and he'll tell you that while material stock comes in
Imperial units, fastener sizes are specified in standard fractions of
inches, and so forth, all his actual machining work is done with the "thou"
as the base unit.  A thou is 1/1000 of an inch.  A milli-inch, that is, but
it's pronounced "thou".  (For real precision work, it's necessary to
consider "tenths" as well, where a tenth is 1/10000 of an
inch.)  A machinist will say things like "this needs to be 500 wide", not
"half an inch wide".

(As an example of an engineering advantage of metric standards, if you're
drilling a hole that's to be tapped for a standard #8-32 screw thread, you
need to use a .136 drill (also known as a #29 drill).  There are tables to
look this up.  For a metric M4x0.5 screw (very close to an
#8-32 in size), I don't need a table to know to use a 3.5mm drill.)

Also: "serious disadvantage"?  Only to the extent that you're either working
with tools and material that are in Imperial units, or you've grown up with
Imperial units, and have no intuition for the metric.
That's just saying that trying to change confers disadvantage, which of
course it does.  It's not an inherent problem with the metric system.

You sound like one of those people who go "Metric? Hah! When people ask me
how far it is to the post office, I say 'about a mile'.  I don't say 'about
1.609 kilometers'", and think they've made a valid argument.

-tih
--
Most people who graduate with CS degrees don't understand the significance
of Lisp.  Lisp is the most important idea in computer science.  --Alan Kay
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