What are 6.5 Digit Multimeters Good For?

It's interesting to calculate the resistance of traces and actually
measure them. Most pcb houses skimp on plating, so when you specify "1
oz" copper, you seldom get it.

On Mon, 15 Mar 2010 20:17:05 -0700, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:

On Mon, 15 Mar 2010 19:53:04 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 15 Mar 2010 19:47:01 -0700, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:

On Mon, 15 Mar 2010 12:11:23 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 12 Mar 2010 18:56:02 -0800, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:

On Fri, 12 Mar 2010 15:23:12 -0800, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:


Except that you never get too much copper... always too little.

John


Maybe from your board house, dipshit.

Measure the sheet resistivity of traces on a few of your boards and
tell us what you see.

John


You do know that we do not use copper boards any more, right?

I didn't know that. What do you use?

John

It is an RoHS world, John. What do you think we use?

What does RoHS have to do with Copper, AlwaysWrong?

It ain't HASL over Copper or SMOBC, I'll tell ya.

IOW, you don't know.

It's interesting to calculate the resistance of traces and actually
measure them. Most pcb houses skimp on plating, so when you specify "1
oz" copper, you seldom get it.

The only place copper is plated is in the holes. The 1 oz copper layer for
traces is a copper sheet that is laminated to the board. It's rolled out to
the proper 1.4 mil thickness when it's manufactured. It's not plated on by
the PCB manufacturer.

You may be making measurement errors when you measure the traces, 1 amp can
be a lot of current on small traces and you may be heating that trace up
quite a bit. Copper has a substantial thermal coefficient of resistance,
heat it up by 25C and the resistance goes up 10%. Try dropping your current
to 0.1A and see how your measurements change.

On Sun, 14 Mar 2010 18:32:13 -0700,
"JosephKK"<quiettechblue_at_yahoo.com> wrote:

On Sun, 14 Mar 2010 00:36:08 GMT, Jan Panteltje <pNaonStpealmtje_at_yahoo.com> wrote:

On a sunny day (Sat, 13 Mar 2010 08:13:20 -0600) it happened John Fields
jfields_at_austininstruments.com> wrote in
l37np519aum4a3r6n9aetaona9ij7hesm7_at_4ax.com>:

On Sat, 13 Mar 2010 13:27:35 GMT, Jan Panteltje
pNaonStpealmtje_at_yahoo.com> wrote:

On a sunny day (Fri, 12 Mar 2010 13:00:04 -0800) it happened D from BC
myrealaddress_at_comic.com> wrote in <MPG.26044b27299d843e9896f7_at_209.197.12.12>:

In article <hne8fg$uqm$1_at_news.albasani.net>, pNaonStpealmtje_at_yahoo.com
says...

On a sunny day (Fri, 12 Mar 2010 10:50:48 -0600) it happened John Fields
jfields_at_austininstruments.com> wrote in
ekrkp5lg8obtcmftn2tmq8adsnlte9u59e_at_4ax.com>:

On Fri, 12 Mar 2010 12:30:31 GMT, Jan Panteltje
pNaonStpealmtje_at_yahoo.com> wrote:

On a sunny day (Thu, 11 Mar 2010 17:56:35 -0800) it happened D from BC
myrealaddress_at_comic.com> wrote in <MPG.26033f321480b139896e5_at_209.197.12.12>:

6.5 digit multimeters sell around $1000.00.
For electronics development, are these $1000 multimeters really
necessary?
What are they good for?

They are not needed, all you need is a 5 Euro multimeter,
and in extreme cases a precise reference.
That means if you use one of those reference chips, you borrow
the very accurate multimeter for a day, measure your reference chip,
write it down, and use that to calibrate your cheap multimeter,
or o compute it's real value,
Saved: 1000$

---
If you don't _need_ the accurate multimeter, then how do you get around
the fact that unless you use _it_ to measure the reference, your cheap
multimeter is pretty much a boat anchor?


JF

Sorry can you explain that again in electronics English?

He means you still need an accurate tool to make use of a less accurate
tool. Which raises the question, why have the less accurate tool?

btw... Boat anchor is a term I sometimes use for large heavy antiqued
test equipment.
Pre LCD scopes are boat anchors.

Yes, OK, but Fields did not read very well,
you only need the accurate one ONCE.
And that means you can go to a place and have yor reference measured.

---
You seem to be the one having trouble with the language since even if
it's used only once, you still _need_ the higher accuracy instrument in
order to determine the error in the lower accuracy one.

JF

No you do not, how do you think those instruments came about?
In your theory nothing could ever be made.
:-)

You are missing some concepts here.
There are things called reference cells, the voltage across the
terminals is dependant on the chemistry/physics. Similar to and
far lower tech to make than bandgap references. The terminal
voltage can be determined to 6 places before putting the meter
leads to them and are repeatable and reliable.
Ratiometric methods can maintain resolution and accuracy in a large
variety of situations, see R/2R DAC systems.
With these concepts in hand you would not have bothered to make your
comment.
Or maybe you do not credit anyone else with these few bits of
typical electrical engineering knowledge.


Do people still use standard cells?

John

On Sun, 14 Mar 2010 18:46:36 -0700,
"JosephKK"<quiettechblue_at_yahoo.com> wrote:

On Fri, 12 Mar 2010 10:44:39 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:

On Fri, 12 Mar 2010 09:33:25 -0800, D from BC
myrealaddress_at_comic.com> wrote:

In article <hndc5b$37k$1_at_news.albasani.net>, pNaonStpealmtje_at_yahoo.com
says...

On a sunny day (Thu, 11 Mar 2010 17:56:35 -0800) it happened D from BC
myrealaddress_at_comic.com> wrote in <MPG.26033f321480b139896e5_at_209.197.12.12>:

6.5 digit multimeters sell around $1000.00.
For electronics development, are these $1000 multimeters really
necessary?
What are they good for?

They are not needed, all you need is a 5 Euro multimeter,
and in extreme cases a precise reference.
That means if you use one of those reference chips, you borrow
the very accurate multimeter for a day, measure your reference chip,
write it down, and use that to calibrate your cheap multimeter,
or o compute it's real value,
Saved: 1000$

Of course there are exceptions,
but in places where that counts they usually have a lot of ++++expensive stuff anyways.
Usually places where nothing really useful is done, like in CERN, or ITER, or LIGO,
etc.

How about mohm measurements? Maybe that's handy.
My DMM only goes to 0.1 ohm.
I thought of measuring DCR of coils or pcb trace resistance for sim
accuracy.



Measuring milli-Ohms is tricky. Ideally you'd like 4-point-probe
measuring... voltage "viewing" pins are separate from current forcing
pins.

I'd do it with an AC current source, so you can gain-up the resulting
voltage.

...Jim Thompson

So, you know some interesting tricks to make an AC current source
accurate to 0.01%? A lot of people would interested, especially if
it was a clean sine source. With a good clean DC current source i
have seen measurements all the way to 0.00002%. There be tradeoffs
here.

Why do need "accuracy" to 0.01%? What are you trying to measure to
that kind of accuracy?

...Jim Thompson

On Mon, 15 Mar 2010 22:26:58 -0500, "krw_at_att.bizzzzzzzzzzzz"
krw_at_att.bizzzzzzzzzzzz> wrote:

On Mon, 15 Mar 2010 20:17:05 -0700, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:

On Mon, 15 Mar 2010 19:53:04 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 15 Mar 2010 19:47:01 -0700, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:

On Mon, 15 Mar 2010 12:11:23 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 12 Mar 2010 18:56:02 -0800, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:

On Fri, 12 Mar 2010 15:23:12 -0800, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:


Except that you never get too much copper... always too little.

John


Maybe from your board house, dipshit.

Measure the sheet resistivity of traces on a few of your boards and
tell us what you see.

John


You do know that we do not use copper boards any more, right?

I didn't know that. What do you use?

John

It is an RoHS world, John. What do you think we use?

What does RoHS have to do with Copper, AlwaysWrong?

The field is called "intermetallics". I wouldn't expect a ditz like
you to get it, always-fucked-in-the-head.

It ain't HASL over Copper or SMOBC, I'll tell ya.

IOW, you don't know.

You wouldn't know what I know. You never will. You are pathetic,
Williams.

It's interesting to calculate the resistance of traces and actually
measure them. Most pcb houses skimp on plating, so when you specify "1
oz" copper, you seldom get it.

The only place copper is plated is in the holes. The 1 oz copper layer for
traces is a copper sheet that is laminated to the board. It's rolled out to
the proper 1.4 mil thickness when it's manufactured. It's not plated on by
the PCB manufacturer.

You may be making measurement errors when you measure the traces, 1 amp can
be a lot of current on small traces and you may be heating that trace up
quite a bit. Copper has a substantial thermal coefficient of resistance,
heat it up by 25C and the resistance goes up 10%. Try dropping your current
to 0.1A and see how your measurements change.

You may be making measurement errors when you measure the traces, 1 am
can
be a lot of current on small traces and you may be heating that trace up
quite a bit. Copper has a substantial thermal coefficient of resistance,
heat it up by 25C and the resistance goes up 10%. Try dropping you
current
to 0.1A and see how your measurements change.

I think my measurements are accurate, and I often include a test trace
whose geometry is suitable for accurate sheet resistance measurement.

If I include a fab note demanding a minimum sheet resistance, or say
"START WITH 1 OZ COPPER" I usually get below 600 uohms/square. If I
just say "COPPERCLAD 1 OZ" I usually don't.

You may be making measurement errors when you measure the traces, 1 amp
can
be a lot of current on small traces and you may be heating that trace up
quite a bit. Copper has a substantial thermal coefficient of resistance,
heat it up by 25C and the resistance goes up 10%. Try dropping your
current
to 0.1A and see how your measurements change.

I think my measurements are accurate, and I often include a test trace
whose geometry is suitable for accurate sheet resistance measurement.

If I include a fab note demanding a minimum sheet resistance, or say
"START WITH 1 OZ COPPER" I usually get below 600 uohms/square. If I
just say "COPPERCLAD 1 OZ" I usually don't.

Well if you are sure you are not heating your traces up when you measure
them it sounds like you need to talk to your fab about the issue. Get them
to explain their fabrication process and what the variables are that can
affect the sheet resistance. 1 oz copper is just an arbitrary standard,
what's important is to know what sheet resistance you can expect out of
them and how variable it can be. It's good to know what the sheet
resistances and dielectric constants of all the board options they offer so
you can get what you need out of them. If it's an important aspect of your
board design you have to specify it, you can't leave it to chance since
they may change suppliers, or processing, or subcontract it out etc. Talk
to them, find out what the options are and what they are comfortable with.
If you are not satisfied find another fab.

What fab are you using?

---------------------------------------
Posted through http://www.Electronics-Related.com

On Sun, 14 Mar 2010 17:54:07 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:

On Sun, 14 Mar 2010 18:46:36 -0700,
"JosephKK"<quiettechblue_at_yahoo.com> wrote:

On Fri, 12 Mar 2010 10:44:39 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:

On Fri, 12 Mar 2010 09:33:25 -0800, D from BC
myrealaddress_at_comic.com> wrote:

In article <hndc5b$37k$1_at_news.albasani.net>, pNaonStpealmtje_at_yahoo.com
says...

On a sunny day (Thu, 11 Mar 2010 17:56:35 -0800) it happened D from BC
myrealaddress_at_comic.com> wrote in <MPG.26033f321480b139896e5_at_209.197.12.12>:

6.5 digit multimeters sell around $1000.00.
For electronics development, are these $1000 multimeters really
necessary?
What are they good for?

They are not needed, all you need is a 5 Euro multimeter,
and in extreme cases a precise reference.
That means if you use one of those reference chips, you borrow
the very accurate multimeter for a day, measure your reference chip,
write it down, and use that to calibrate your cheap multimeter,
or o compute it's real value,
Saved: 1000$

Of course there are exceptions,
but in places where that counts they usually have a lot of ++++expensive stuff anyways.
Usually places where nothing really useful is done, like in CERN, or ITER, or LIGO,
etc.

How about mohm measurements? Maybe that's handy.
My DMM only goes to 0.1 ohm.
I thought of measuring DCR of coils or pcb trace resistance for sim
accuracy.



Measuring milli-Ohms is tricky. Ideally you'd like 4-point-probe
measuring... voltage "viewing" pins are separate from current forcing
pins.

I'd do it with an AC current source, so you can gain-up the resulting
voltage.

...Jim Thompson

So, you know some interesting tricks to make an AC current source
accurate to 0.01%? A lot of people would interested, especially if
it was a clean sine source. With a good clean DC current source i
have seen measurements all the way to 0.00002%. There be tradeoffs
here.

Why do need "accuracy" to 0.01%? What are you trying to measure to
that kind of accuracy?

...Jim Thompson

Perhaps i wanted to get credible results on contact resistance
repeatability. Or maybe i need to verify a current measuring shunt.

On Sun, 14 Mar 2010 17:54:07 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:

On Sun, 14 Mar 2010 18:46:36 -0700,
"JosephKK"<quiettechblue_at_yahoo.com> wrote:

On Fri, 12 Mar 2010 10:44:39 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:

On Fri, 12 Mar 2010 09:33:25 -0800, D from BC
myrealaddress_at_comic.com> wrote:

In article <hndc5b$37k$1_at_news.albasani.net>, pNaonStpealmtje_at_yahoo.com
says...

On a sunny day (Thu, 11 Mar 2010 17:56:35 -0800) it happened D from BC
myrealaddress_at_comic.com> wrote in <MPG.26033f321480b139896e5_at_209.197.12.12>:

6.5 digit multimeters sell around $1000.00.
For electronics development, are these $1000 multimeters really
necessary?
What are they good for?

They are not needed, all you need is a 5 Euro multimeter,
and in extreme cases a precise reference.
That means if you use one of those reference chips, you borrow
the very accurate multimeter for a day, measure your reference chip,
write it down, and use that to calibrate your cheap multimeter,
or o compute it's real value,
Saved: 1000$

Of course there are exceptions,
but in places where that counts they usually have a lot of ++++expensive stuff anyways.
Usually places where nothing really useful is done, like in CERN, or ITER, or LIGO,
etc.

How about mohm measurements? Maybe that's handy.
My DMM only goes to 0.1 ohm.
I thought of measuring DCR of coils or pcb trace resistance for sim
accuracy.



Measuring milli-Ohms is tricky. Ideally you'd like 4-point-probe
measuring... voltage "viewing" pins are separate from current forcing
pins.

I'd do it with an AC current source, so you can gain-up the resulting
voltage.

...Jim Thompson

So, you know some interesting tricks to make an AC current source
accurate to 0.01%? A lot of people would interested, especially if
it was a clean sine source. With a good clean DC current source i
have seen measurements all the way to 0.00002%. There be tradeoffs
here.

Why do need "accuracy" to 0.01%? What are you trying to measure to
that kind of accuracy?

...Jim Thompson

Perhaps i wanted to get credible results on contact resistance
repeatability. Or maybe i need to verify a current measuring shunt.

On Tue, 16 Mar 2010 05:02:11 -0700,
"JosephKK"<quiettechblue_at_yahoo.com> wrote:

On Sun, 14 Mar 2010 17:54:07 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:

On Sun, 14 Mar 2010 18:46:36 -0700,
"JosephKK"<quiettechblue_at_yahoo.com> wrote:

On Fri, 12 Mar 2010 10:44:39 -0700, Jim Thompson
To-Email-Use-The-Envelope-Icon_at_My-Web-Site.com> wrote:

On Fri, 12 Mar 2010 09:33:25 -0800, D from BC
myrealaddress_at_comic.com> wrote:

In article <hndc5b$37k$1_at_news.albasani.net>,
pNaonStpealmtje_at_yahoo.com says...

On a sunny day (Thu, 11 Mar 2010 17:56:35 -0800) it happened D
from BC <myrealaddress_at_comic.com> wrote in
MPG.26033f321480b139896e5_at_209.197.12.12>:

6.5 digit multimeters sell around $1000.00.
For electronics development, are these $1000 multimeters really
necessary?
What are they good for?

They are not needed, all you need is a 5 Euro multimeter,
and in extreme cases a precise reference.
That means if you use one of those reference chips, you borrow
the very accurate multimeter for a day, measure your reference
chip, write it down, and use that to calibrate your cheap
multimeter, or o compute it's real value,
Saved: 1000$

Of course there are exceptions,
but in places where that counts they usually have a lot of
++++expensive stuff anyways. Usually places where nothing really
useful is done, like in CERN, or ITER, or LIGO, etc.

How about mohm measurements? Maybe that's handy.
My DMM only goes to 0.1 ohm.
I thought of measuring DCR of coils or pcb trace resistance for
sim accuracy.



Measuring milli-Ohms is tricky. Ideally you'd like 4-point-probe
measuring... voltage "viewing" pins are separate from current
forcing pins.

I'd do it with an AC current source, so you can gain-up the
resulting voltage.

...Jim Thompson

So, you know some interesting tricks to make an AC current source
accurate to 0.01%? A lot of people would interested, especially if
it was a clean sine source. With a good clean DC current source i
have seen measurements all the way to 0.00002%. There be tradeoffs
here.

Why do need "accuracy" to 0.01%? What are you trying to measure to
that kind of accuracy?

...Jim Thompson

Perhaps i wanted to get credible results on contact resistance
repeatability. Or maybe i need to verify a current measuring shunt.

If you do some kind of 4-point measuring arrangement, contact
resistance doesn't matter.

...Jim Thompson

On Mon, 15 Mar 2010 22:26:58 -0500, "krw_at_att.bizzzzzzzzzzzz"
krw_at_att.bizzzzzzzzzzzz> wrote:

On Mon, 15 Mar 2010 20:17:05 -0700, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:

On Mon, 15 Mar 2010 19:53:04 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:

On Mon, 15 Mar 2010 19:47:01 -0700, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:

On Mon, 15 Mar 2010 12:11:23 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 12 Mar 2010 18:56:02 -0800, Archimedes' Lever
OneBigLever_at_InfiniteSeries.Org> wrote:

On Fri, 12 Mar 2010 15:23:12 -0800, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:


Except that you never get too much copper... always too little.

John


Maybe from your board house, dipshit.

Measure the sheet resistivity of traces on a few of your boards and
tell us what you see.

John


You do know that we do not use copper boards any more, right?

I didn't know that. What do you use?

John

It is an RoHS world, John. What do you think we use?

What does RoHS have to do with Copper, AlwaysWrong?

The field is called "intermetallics". I wouldn't expect a ditz like
you to get it, always-fucked-in-the-head.

It ain't HASL over Copper or SMOBC, I'll tell ya.

IOW, you don't know.

You wouldn't know what I know. You never will.

You are pathetic, Williams.

On Tue, 16 Mar 2010 00:06:53 -0500, "Randomly"
fburfell2000_at_n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote:

It's interesting to calculate the resistance of traces and actually
measure them. Most pcb houses skimp on plating, so when you specify "1
oz" copper, you seldom get it.

The only place copper is plated is in the holes. The 1 oz copper layer for
traces is a copper sheet that is laminated to the board. It's rolled out to
the proper 1.4 mil thickness when it's manufactured. It's not plated on by
the PCB manufacturer.

You may be making measurement errors when you measure the traces, 1 amp can
be a lot of current on small traces and you may be heating that trace up
quite a bit. Copper has a substantial thermal coefficient of resistance,
heat it up by 25C and the resistance goes up 10%. Try dropping your current
to 0.1A and see how your measurements change.

I think my measurements are accurate, and I often include a test trace
whose geometry is suitable for accurate sheet resistance measurement.

If I include a fab note demanding a minimum sheet resistance, or say
"START WITH 1 OZ COPPER" I usually get below 600 uohms/square. If I
just say "COPPERCLAD 1 OZ" I usually don't.

John


The sheets are 4' x 8' and the cladding is industry standard, you dopey

On Tue, 16 Mar 2010 06:58:50 -0700, John Larkin
jjlarkin_at_highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 16 Mar 2010 00:06:53 -0500, "Randomly"
fburfell2000_at_n_o_s_p_a_m.n_o_s_p_a_m.yahoo.com> wrote:

It's interesting to calculate the resistance of traces and actually
measure them. Most pcb houses skimp on plating, so when you specify "1
oz" copper, you seldom get it.

The only place copper is plated is in the holes. The 1 oz copper layer for
traces is a copper sheet that is laminated to the board. It's rolled out to
the proper 1.4 mil thickness when it's manufactured. It's not plated on by
the PCB manufacturer.

You may be making measurement errors when you measure the traces, 1 amp can
be a lot of current on small traces and you may be heating that trace up
quite a bit. Copper has a substantial thermal coefficient of resistance,
heat it up by 25C and the resistance goes up 10%. Try dropping your current
to 0.1A and see how your measurements change.

I think my measurements are accurate, and I often include a test trace
whose geometry is suitable for accurate sheet resistance measurement.

If I include a fab note demanding a minimum sheet resistance, or say
"START WITH 1 OZ COPPER" I usually get below 600 uohms/square. If I
just say "COPPERCLAD 1 OZ" I usually don't.

John


The sheets are 4' x 8' and the cladding is industry standard, you dopey
ditz! I know because my dad made some of the very first machines that
were used by the industry to make the current form factor boardstock.
That would be Cincinnati Milacron, Inc., which at the time would have
been named The Cincinnati Milling Machine Company. There are not very
many products you could name that didn't use Cincinnati machines. Fuller
brush company... Your hair brush injection molders. Ebonite... Your
bowling balls, GE jet engines, FMC corp M1-A1 MBTs. All three US auto
makers. The list goes on for hundreds of brands, products, industries.
Now, most companies have bought Japanese machining centers. Milacron
probably not doing so well... lemmie check real quick... DAMN! They
have been bought out by a conglomerate with private stock! MAG
Industrial Automation owns Milacron now! Oh well, they were the guys.

If you are getting it thinner, then your PCB house... isn't one. They
should know how to correctly clean a PCB without losing copper. Also,
your measurement accuracy can be off due to you not performing the test
completely correctly.

Kind of like the vapor phase thing. It works for you, so you do not
care if you are actually doing it right or not.

Sorry, but in this case, if you do not know where the error(s) get(s)
introduced, you will knot know what your resultant figures mean, nor how
to offset them properly to correct for the errors that get introduced in
to the not quite ideal test scenario.

Not ideal? What is the bad element? YOU, Johnny boy.

All it would take is a single mistake, and the difference you refer to
(600 as compared to 1000) is very likely completely due to said error.

I'd say that even though you think you are, you have failed to
compensate for the lead resistance of your test. What you should do is
apply a current and measure the voltage between the NUT (NodeSpan Under
Test). Far better than you thinking that you can measure micro-ohms
accurately, much less properly.