Robert Roland wrote on 9/1/2017 2:51 PM:
On Fri, 1 Sep 2017 03:50:38 -0400, rickman wrote:

Six foot skis are very convenient, but 180 cm are not
so much.

Why do you think that is? Because that's what you are USED TO, of
course. If you told me you skis are "six foot" long, I would have no
clue if they were too long or too short for me. If you told me they
are "one eighty", I'd know right away.

I'm not talking about the familiarity of the units, I'm talking about the
convenience. Just like the Brits still use stones for weight because they
don't need the precision of knowing they are 224 pounds, but 16 stone is
very handy.


If you told me they are 1800 mm long, I'd still know right away. If I
told you they are 72 inches, you'd have to think about it for a
second. It is more convenient to move a decimal separator than to
divide by 12.

Now you are getting close. I buy stuff on ebay and it is not uncommon to
see dimensions of 4 digits in mm when it would be more convenient in dm or
even just meters, but easily more convenient in feet or inches. mm are far
more precise than needed for most measurements and awkward to scribe on
rulers since the lines need to be so thin they are hard to see. I expect
tape measures are graduated in 2 mm divisions. If they aren't, they should be.


Another example, PCB traces are still measured in thousandths of
an inch even when working with metric sized boards because the numbers are
much more convenient, i.e. 6/6 vs. 0.1524 mm.

You've got it all backwards. I would make that trace 0.15 mm, which is
much more convenient than 5.90551181 thousandths of an inch.

Obviously, the inch is more convenient when you choose an example that
is a nice, round fraction of an inch.

I would love for all PCB measurements to be metric since the parts on the
board are all metric. But I don't write the software and I don't design the
web interfaces that 90% use mils and not metric. Now that trace/space
measurements are getting to be fractions of mils, we may see that change,
but small unit numbers are always more convenient than fractions or large
numbers. That's why we have wire gauge, etc.


Your example uses a unit that is ONE THOUSANDTH of an inch. You can't
do that. The thousand (and the hundred and the ten) belongs to the
metric system. The imperial system uses halves, quarters, eighths and
so on. Your trace is roughly 3/512 of an inch if you were to stick to
your system.

Ok, I'll inform the world. World! Consider yourself on notice!!! No more
use of mils or micro-inches!

--

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998