this post was submitted on 30 Mar 2025
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[–] [email protected] 42 points 1 day ago (3 children)

That level of precision in a resistor would literally be thrown off if you breathed on it. If you actually needed that, then you need to build an extremely controlled environment around it. Even then, the heat from the electricity itself would throw it off. Maybe in a liquid nitrogen bath?

[–] [email protected] 19 points 19 hours ago (1 children)

First, assume a spherical resistor in a vacuum, that can also dissipate heat with 100% efficiency.

Now that we’re in physics land, anything is possible.

[–] [email protected] 1 points 17 hours ago

Only if it isn't applied physics.

[–] [email protected] 23 points 1 day ago* (last edited 1 day ago)

Its funny the first thing I thought of was, at what temperature.

[–] [email protected] 3 points 18 hours ago (1 children)

A big aspect of good design is being able to solve an issue as succinctly as possible, with as wide an operating range as possible. Lower tolerance requirements = better.

If you need that level of precision, you might want to reconsider your career in circuit design.

[–] [email protected] 1 points 18 hours ago (1 children)

You can't tell me that there isn't a good reason that 0.001% resistors exist. Otherwise why sell them?

[–] [email protected] 3 points 16 hours ago

4 Sig figs vs 9 Sig figs is a big gap. If you need your resistors in a circuit to be precise to 9 Sig figs, seek a new career.

It is almost always possible to take a system and make it more precise by using more precise parts (just gotta make sure you know what part you are changing to improve what tolerance). You do get diminishing returns with that, but it beats inventing a new system if the tolerances you need are just alittle ways away.

[–] [email protected] 68 points 1 day ago (5 children)

I'm a physicist. If you are an engineer that sounds like a "you" problem.

[–] [email protected] 3 points 14 hours ago

Too true, and my problem is about to be your problem and the cycle continues comrade.

[–] [email protected] 7 points 23 hours ago

OK, the solution is "how accurate will make the physicist and accountants both only kinda mad"

[–] [email protected] 36 points 1 day ago (1 children)

Not using the correct resistors does cause a U problem every once in a while.

[–] [email protected] 10 points 1 day ago

Or an I problem, depending on your perspective

[–] [email protected] 18 points 1 day ago (1 children)

Sounds like a 6 ohm resistor solution.

[–] [email protected] 10 points 1 day ago

They're 5.6 or 6.8 ohms usually

[–] [email protected] 7 points 1 day ago (1 children)
[–] [email protected] 13 points 1 day ago

This is also a "you" problem. Fix that at your earliest convenience.

[–] [email protected] 37 points 1 day ago (2 children)

i miss old school radioshack. i did not know what all those bins of tiny electronic hobby parts were for, but I desperately wanted to learn. I did eventually but you have to get all your stuff from some shady oligarch.

[–] [email protected] 7 points 22 hours ago

i did not know what all those bins of tiny electronic hobby parts were for, but I desperately wanted to learn.

From what I understand, prior to the personal computer boom of the 1980's, HAM radio was kind of a big deal with nerds. The parts were there for all manner of electronics tinkering, but a big mainstay was building and modifying radios. Yeah, you had people tinkering with computers in the 1970's too, but it was more niche (until it wasn't).

[–] [email protected] 16 points 1 day ago

Yeah we’re living in the ruins of the old America already and have been for like 25 years.

It’s dirty they just use the same business names they did in the 20th century. While making smoke and mirrors versions of the old products.

[–] [email protected] 77 points 1 day ago (1 children)

Without using fancy components: Just simply adding a 6.2 and a 2400 Ohm resistor in parallel already gives you 6.18402 Ohm ⚡️

[–] [email protected] 28 points 1 day ago (3 children)

Real world resistors usually have a tolerance of ±5%, so you'll never get anything that precise.

[–] [email protected] 37 points 1 day ago* (last edited 1 day ago) (6 children)

That's why I keep a roll of 20 AWG nichrome on hand. Spool off 9.7195853528209 feet and it'll be bang on.

[–] [email protected] 5 points 1 day ago (1 children)

So 1 inch of your wire would weigh ~0.0987 grams, so to measure down to 8.6350242338508 inches of wire your scale would need to weigh down to ~0.00000000000007 grams. Which is the weight of about a dozen atoms or so.

[–] [email protected] 10 points 1 day ago (1 children)

Yeah which is why you use a Kibble balance. Are you sure you're cut out for this kind of work?

[–] [email protected] 3 points 1 day ago (1 children)

I'm not a scientist, I'm just in IT haha

I figured there was a way to measure that small of weight but I didn't know!

[–] [email protected] 3 points 1 day ago

Its akin to having an electon microscope in your kitchen

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[–] [email protected] 12 points 1 day ago

I've actually found 1% to be a lot more common nowadays.

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[–] [email protected] 135 points 1 day ago (24 children)

Just put two π ohm resistors in series duh

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[–] [email protected] 52 points 1 day ago (7 children)

Numbers like that are why I quit majoring in mechanical engineering. Physics took the beauty of math and made it ugly.

You knew something was wrong in calculus when you got a fucked up coefficient that wasn’t a nice number.

[–] [email protected] 10 points 1 day ago (1 children)

The trick is to round everything. Pi? Basically 3.

[–] [email protected] 7 points 1 day ago (1 children)

I've heard a story (so like 4th hand at this point) where an astrophysicist was talking about galaxy rotations or something. "And for this model, we can simplify pi to 10."

[–] [email protected] 2 points 19 hours ago

My thermodynamics professor made so approximations in his derivations that all of his equations had an “O” term to represent the inaccuracy. Every time he made another approximation he’d say “and, of course, the O sucks up the error”.

[–] [email protected] 54 points 1 day ago (5 children)

Numbers like that should have been why you kept going in mech E.

Once you get past the educational stage, every one of those calculations becomes "OK now round to the closest whole number that gives you the larger factor of safety and move on"

[–] [email protected] 35 points 1 day ago (3 children)

Using π = 4 is only a 27% safety margin, better go for π = 10 just to be safe.

[–] [email protected] 21 points 1 day ago (4 children)

Pi r square, square have 4 sides. No problem found.

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[–] [email protected] 2 points 22 hours ago

The difficult part of engineering is figuring out what number you have to round then multiply by 1.2 or 0.8

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[–] [email protected] 10 points 1 day ago* (last edited 1 day ago)

After calculus though, they just expect you to cope with fucked up coefficients. In Diff Eq, sometimes you do just get something like 3/111 cos (6/111 x). It gets harder to come up with examples that work out with nice integers.

Physics can also have some really beautiful math, look at Lissajous figures. Once you understand the connections between e, the imaginary plane, and sine/cosine, you get some profound understandings about how electric and magnetic fields work.

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[–] [email protected] 76 points 1 day ago (13 children)

couldnt you technically fine tune a potentiometer to be this resistance if you were precise enough?

[–] [email protected] 70 points 1 day ago

Mathematically yes. Practically, right now? No.

So you need a resistor of this value for your widget.

For that many places of precision you're looking at a potentiometer with a 10 nano-ohm precision.

I am not aware of any commercially available resistor that can do that but you could create one using microelectronic structures used for ICs and derive a 10 nano-ohm resistor by design and then chain enough of these elements into a resistor network or potentiometer to create the super precise resistance value you want.

Cool, congratulations.

Now how are you going to use this 10 nano-ohm resistor? What voltage will you be applying across it? What current do you expect it to handle? And therefore what are your power requirements? What are your tolerances, how much can the true value deviate from the designed ideal?

Because power generates heat through losses, and that will affect the resistance value so how tightly do you need to manage the power dissipation?

How will you connect to this resistor to other circuit components? Because a super precise resistor on it's own is nothing but an over-engineered heating element.

If you tried connecting other surface mount devices (SMDs) from the E24 or even E96 series to this super precise resistor then the several orders of magnitude wider tolerances of these other components alone will swallow any of the precision from your super accurate resistor.

So now your entire circuit has to be made to the same precision else all of your design work has been wasted.

Speaking of which, now your heat management solution now needs to be super precise as well and before you know it you've built the world's most accurate widget that probably took billions of dollars/euros/schmeckles and collaboration from the worlds leading engineers and scientists that probably cost more time and money than the Large Hadron Collider.

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