I have an old analogue stopwatch with three dials. One measures minutes (+/- 0.5 min), a seconds dials (+/- 0.5 s), and a dial measuring 1 s in 0.1 s intervals (+/- 0.05 s). If I used this stopwatch to record a measurement, would the overall precision be +/- 30.55 s?

I know that it is the distance light travels in a vacuum in 1\299,792,458 of a second. But the number 299,792,458 is speed of light measured in meter/sec so you need to define meter to define meter/sec to define meter so how does it work .

(Am I thinking some nonsense?)

Preface:

I'm european, I grew up with metric and use it daily, so please take my question rhetorically, I'm not asking out of ignorance.

I simply can't shake the feeling that we're sometimes putting a lipstick on a pig a little bit.

I'm mainly looking for opinions and different philosophical points of view.

Metric is considered good because:

1. Complex units are composed of basic units: N = kg * m * s^-2
2. Units of different sizes can be made by multiplying by powers of 10, with the power signified by the prefixes like mega, kilo, milli, etc.

I strongly agree with the advantages of the first point. Arguably, the plank system is even "cleaner", but metric is still great in this regard.

But the second point is what people often focus on, and I don't see much advantage in that, if any at all.

I don't think it's bad, I just think it's neutral, and perhaps even somewhat unnecessary.

2kg means 2000 grams, because kilo means thousand.

So,

2kg =

2 * kilo * gram =

2 * thousand * gram.

It seems to me like we're still just giving the answer in grams. We're merely replacing the english word for the 10ⁿ part with the Greek/Latin equivalents.

I can say "thousand" instead of "kilo", and then it doesn't matter if I'm talking about litres, watts or becquerels.

One could argue that for negative powers it's much easier to say

12 millimetres

compared to

12 thousandths of a meter

but that says more about awkwardness of english grammar rules rather than the prefixes achieving something new.

Comparing the number of syllables with the english words,

"deka" is worse than "ten" or the "...ty" suffix ("three dekagrams" vs "thirty grams")

"hekto" and "kilo" is same length as "hundred" and "thousand",

above that, metric has less syllables, therefore prefferable.

For negative powers, english adds the "of a", as in, "tenth of a Joule", so metric will always win.

But if we really cared about syllables so much, we'd have renamed "kilometre" a long time ago.

Also, we would have to appreciate the words being shorter in the imperial system.

To me, the real advantage of metric prefixes seems to come from everybody strictly agreeing to always use metres for length, and not mix in any other length units with non-10ⁿ ratios.

Also, the prefixes are internationally recognized, which is a plus, but it's an argument from popularity.

Am I missing something here?

Is there some other advantage of the prefixes I'm not considering?

Maybe we should create a universal easy-to-say international number system, and then we won't even need the metric prefixes.

The idea of metric time was an idea of changing the system of time to divide:

Day into 10 decimal hours (8 640 s)

Decimal hour into 100 decimal minutes (86.4 s)

Decimal minute into 100 decimal seconds (0.864 s)

And it looks good.

Someone will say: "second must be that length, because it is perfect for counting"

No it isn't, I never counted to 10 in 10 seconds.

But I have a few suggestions:

1st. Rename decimal second to something shorter like "decsec" and make it a base unit

2nd. Add myria- prefix for 10⁴ to replace decimal hour with myriadecsec. Myria- was actually a prefix till 1960. Add 10⁵ prefix, I guess lakha- would be cool, but I'm biased towards calling it insta- (because quintal would be instagram) and day would be just lakhadecsec. (But calling it a day it's also ok) Also decimal minute would be hectodecsec

3rd. Do NOT make a week 10 days. 1st - it would make work harder, because nobody will give you 6 days of work, and 7-3 scale is too much. 2nd - every 7 day it's sabbath.

4th. Move calendar by 6 years. Jesus was born ~2032 years ago, not 2026. And it makes a weird paradox, where everybody says that Jesus was born in 6 BC, but also everybody says he died in 33 AD, but he was 33 when he died, so it really was 27 AD

So what do you think? Should we rewrite time to 10/100/100, or keep it 24/60/60?

In our world in some places we still don't use metric units. Which is already bad, but most of units have at least some logic and intuition behind them, which at least partially defends it's use. For example:

Land mile is 2000 steps, sometimes I (as an European) use it for measuring steps easily

Nautical mile is 1' of earth circumstance, I can imagine someone using it

Kilogram-force is weight of 1 kilogram on earth, sometimes I use it for measuring weight and pressure (1 kgf/cm² ≈ 1 atmosphere)

Bar is approximately equal to regular Earth atmosphere, so it's kgf/cm² but for those working with pascals

But calorie? It's defined as the energy needed to raise the temperature of 1 g of water by 1 °C. Which is absolutely meaningless. WDYM I need to eat 2000 kcal everyday? So I can have energy to heat 2 megagrams/tonnes of water by 1 °C? Nice to know because it is exactly what I'm gonna do today.

Even Joule is more logical as it's based on distance and force, so I guess it could be interpreted in some way.

Summarizing:

Other non-scientific units are at least intuitive

Calorie isn't

Even Joule would be better

So calorie is dumb at least if your not a kettle

Of course, if you think otherwise, feel free to share your opinion. Bye!

Does anyone know the linear mass density of the wire on the sonometer X164972 that is attached to the newton meter, the one in the centre?

I’m trying to learn the metric system as I plan to move to Canada in the next couple years and am having some trouble finding resources that actually teach instead of just throwing information at me. Anyone know of a good program that will help me learn or have any tips. Imperial is all I know I was born and raised in the USA

So 1cm = inch, 1dm = foot (more like baby foot), 1m = yard, 1km = mile

Also gallon for 1L and pound for 1kg

One of the most common defense for Fahrenheit is smth like this;

"Fahrenheit is more intuitive for human experience. 0 degree is super cold, and 100 degree is super hot! It is just simple as that!"

With that logic, 50 degree Fahrenheit should be the "middle temperature"; which is 10 degree Celsius.

Is it just me or being 50'F/10'C actually feel cold? Such temperature requires sweater at least, and even light jacket sometimes. That is nowhere near the "middle temperature", isn't it? Or am I just weird?

Before I start I wanted to specify that this post would probably change absolutely nothing.

Kilogram is annoying, it's the base unit of SI, but for some reason it has a prefix. It is annoying, because with different units the prefixes work with a cool perk:

If one unit has a prefix, it is moved to the answer: kJ/s = kW

If you are multiplying two units with prefixes, they multiply: kW•ks = MJ

Dividing divides them (obviously): kJ/ks = W

But when base unit has a prefix it doesn't work, and kg•km/s² should be meganewton, but it's NOT, it's kilonewton.

I have a few purely hypothetical ideas:

1st (most obvious) use grams. It would mean that the unit of force would be g•m/s², problem: it would be equal to 1 mN, which is incredibly small, human weighting 700 000 force units would be really small. I'm not even gonna start talking about density with g/m³.

2nd use tonnes. This means that the unit of force would be derived as t•m/s², so it would be equal to 1 kN. There are pros, like: 1. Good for heavy industry, for example: Poland mines 43 million tonnes of coal (instead of billion/milliard kilograms) the weight of a car would be ~15 force units. 2. Density of water is 1 t/m³ which is cool to have a base unit of density to be equal to density of water, also we could stop using g/cm³. But there are cons: tonne is too heavy for everyday life. Human would weight 70 mt (militonne) or 7 ct (centitonne), a slice of bread would weight 40 μt (microtones), so tonne is good for heavy industry, but if you don't want to use mili and micro prefixes, it isn't that great (still not that bad)

3rd grave, grave is suggested unit of mass equal to 1 kg, it was almost accepted, but then they realized that graf is German noble title. There is no nobelty today, so grave would work. It has all pros of kilogram + perks of being a unit without prefixes, so kilograve•km/s² would in fact equal MN (meganewton). It's also good, because all other units can keep their names, grave•m/s² is still 1 N. Let's make a symbol for grave "gv" 1 t = 1 Mg = 1 kgv. 1 kg = 1 gv. 1 g = 1 mg

What do you think guys? In perfect system we would use kilograms, or replace them with grams, tonnes, graves or something else. Share your opinion in the comments

I live in Canada, and we're still a slave to american products. That means anything we produce will be manufactured with imperial dimensions. I'm sick of it.

I've been trying to find perforated aluminium sheet, and it's all imperial. I've been able to find several suppliers in Canada (and overseas), but none of them make a metric product. It makes my design work much more difficult. I have to spend tons of time calculating offsets and doing conversions, it's a huge waste.

Forget about the wider world for a minute. I got myself into 3D printing less than a year ago. I design models, run and tweak slicer software, shop for machines and components (nozzles, etc.) and supplies (filaments, etc.), and watch way too many explainer videos from many online creators.

When I step back from various individual topics in 3D printing, I notice something in the big picture that's easily taken for granted: Everyone uses metric units when describing 3D printing techniques and products, and even use the same unit in almost all domains (with minor variations like g/kg, m/mm/μm). It doesn't matter if the designer, product, or YouTuber is from America, Europe, or Asia - the units are always the same, and I barely know the country of origin unless I dig into details. This is so radically different from older industries and practices, like when you have to worry about whether to use an inch ruler or centimetre ruler, what a "tatami mat" is in Japanese real estate, what a short ton vs. long ton versus metric ton is when shipping large goods, whether you're buying gallons or litres of fuel, whether a recipe is in °C or °F, etc.

So if you're involved in 3D printing, you get a firsthand experience of what it's like when everyone internationally uses the same units, everyone participates in the same discussion and shop in the same marketplace, and you don't have to convert any numbers and units. It's such a breath of fresh air, and I wish other industries would unify their measurements in this way.

Keep in mind that 3D printing is about 20-ish years old, depending on how you look at the history of consumer products vs. industrial products vs. research prototypes. It had the opportunity to start fresh, without much baggage of traditional units and practices, and was born into the Internet-connected world. In terms of measurement units, I think this industry absolutely made the right choices, despite being surrounded by so many pre-existing industries that use non-metric units and continue to make the bad choice of not transitioning to metric.

Here are some examples of real quantities used in 3D printing and described in metric units (left side), versus my hypothetical caricature (based on other industries) of what it would look like if US Customary units are involved (right side):

• Layer height: 0.07 mm, 0.15 mm, 0.25 mm - versus - 3 thou, 6 thou, 10 thou, 3/1024″ (LMAO), 3/512″, 5/512″.
• Nozzle diameter: {0.2, 0.4, 0.6} mm - versus - 0.008″, 0.015″, 0.025″.
• Spool of filament: 1 kg, 3 kg - versus 2.2 lb, 6.6 lb, 2 lb 3 oz, 6 lb 10 oz. (You could choose to sell a nice round number of pounds, but then it would have ugly decimals in kilograms.)
• Random masses of printed objects (slicer software can calculate and show, or physically weigh after printing): {23.7, 98.9, 230, 664} grams - versus - {0.8, 3.5, 8.1, 23.4} oz, {0.05, 0.22, 0.51, 1.46} lb, 1 lb 7.4 oz.
• Random lengths of filament consumed (slicer software can calculate and show): {6.15, 72.7, 364} metres - versus - {242, 2862, 14331}″, {20′ 2″, 238′ 6″, 1194′ 3″}, {20.2, 238.5, 1194.2}′, {6yd 2′ 2″, 79yd 1′ 6″, 398yd 3″} (I thought USC lovers love mixed units?), {6.73, 79.5, 398} yd.
• Build plate printable dimensions: 250 mm × 210 mm = 52 500 mm² - versus - approximately 10″ × 8″ = 80 in², 9 27/32″ × 8 1/4″ = 81.2 in² = 0.564 sq ft.
• Build volume: 153.4 mm × 87 mm × 165 mm = 2 202 057 mm³ = 2.202 L - versus - 6.03″ × 3.43″ × 6.50″ = 134.44 in³ = 74.5 US fl oz = 9.31 US cup = 2.33 US qt = 0.581 US gal.
• Chamber, bed, nozzle temperature: {50, 100, 230} °C - versus - {120, 210, 445} °F.

Extra topics tangentially related:

• I'm glad 3D printing chose millimetres, not centimetre, as the unit of length - because it scales by a power of 1000 from the metre, just like the micrometre, nanometre, kilometre, etc. Before 3D printing existed, the precedent is that serious engineering and metal machining already use millimetres, not centimetres. Advocates for mm over cm include Pat Naughtin (video and long PDF) and the Metric Maven. I could write a full-length post about why centimetres are bad; there really is a lot to say about it.
• I talk about all aspects of my 3D modeling in millimetres exclusively - "this needs a 5.8 mm diameter hole", "the overall part is 200 mm long". Other people might talk about these aspects in customary units, like "1/4-inch hole", "needs 3 inches of clearance", which I find mildly annoying. But even then, these people will never refer to the layer height or nozzle diameter in decimal inches - which is good for the 3D printing community, but inconsistent with their other habits.
• Typical acceleration numbers are written like "20 000 mm/s²", which is equal to 20 m/s². The former isn't wrong, but it's more digits than necessary. And I've seen some people refer to it as "20K mm/s²", which is wrong in multiple ways. This is analogous to the questionable practice of labeling power banks as "10 000 mAh" instead of "10 A⋅h".
• My previous observation about exclusively using degrees Celsius in 3D printing: https://www.reddit.com/r/Metric/comments/1qumhtn/personal_computers_and_3d_printers_use_celsius/

Hi so this is my excel setup for a lab experiment that involves dosing field collected sediment with liquid mercury chloride stock solution ppm (column B) to reach mercury concentrations on dry weight basis (column A). We had to measure the moisture content in the sediment and determined in was 70% water so 30% dry. Originally we tried dosing
250 grams of sediment but our mercury concentrations were way off from our targets so we then we tried dosing 5 grams of sediment. Column G measured or mercury needed in micrograms was achieved by taking out target conc in dry weight (col A ) x by dry weight of sediment (col F) but since we’re adding liquid mercury solution needed to convert to microliters so (amount need in micrograms / stock solution amount) x 1000 … I believe these are accurate conversions , but we keep getting lower mercury concentrations than what we are anticipating, which could also be attributed to how we mixed the solution.Yes I know this is more chemistry related but it does involve a little bit of math and I’m just trying to make sure I’m doing this correctly , thank you !

* note the stock solution already takes account the chloride ions in the mercury solution

Kilowatt-hour is a unit of energy equal to the energy produced by 1 kilowatt of power in one hour of time. It's completely idiotic, because the unit of energy is joule, where joule is newton times metre or watt times second. Let me give an example, for why using kWh over MJ (megajoule) is dumb:

Distance:

Let's use kn (knot, nautical mile per hour, 0,51(4) m/s) as a unit of velocity. Let's assume that steam ship Anne moves with velocity of 50 kn. This boat moves for 1 day. Now calculate the distance. Normal people will say that 50 kn = 50 M/h and 1 d = 24 h therefore 50 kn × 1 d = 50 M/h × 24 h = 50 M × 24 = 1200 M. But with kWh logic it is: 50 kn × 1 d = 50 knd (knot-day). If you think knot-days are dumb, accept that kilowatt-hours are also dumb.

We should get custom units like Megabarrel of oil and kilo cat food unit to measure the amount of kilos of cat food you bought

Why can't Americans just adapt to the metric, they pretend like its this impossible lifestyle change where they have to do 1000 pull ups daily, its not even that hard tbh. Give them one month and their minds will adapt to the metric. And once the newer generation grows up it will be even easier.

"OhHOH But it wIlL cOsT tHEm miLLiOns of DollArs to change EvErY BiLlBoArd", yeah no shit, but even if they give 1% of their military budget for this it would be probably done in a couple of years. Why can't they just switch and get this over with. They have no excuse to not do it.

Also would like to mention their mmddyyyy format.

I live in Australia, where we use the NORMAL metric system. Every time I shop online, like AMZ, the sellers always listing product dimensions and weights exclusively in inches, ounces, and pounds. And as known by everyone, not easy to convert between them. I don't know why, though they deliver to AU, or the rest of USA.

So I only am asking this because I am very confused on this issue that someone is bringing up. To start, my K-8 district did not instruct students in imperial US units, we only used SI from the very beginning, so no inches or yards, just SI. Now I've always been taught that SI is just the modern metric system as it's regulated by the same body that maintained the metric system. I personally use both measurement system interchangeably because being in the US most everyday items are in customary units, but professionally I have to use metric units to calculate a lasers safety rating and other aspects on EH&S.

Like the definition of SI is according to the Bureau International des Poids et Mesures 2019 Brochure

"The SI is a consistent system of units for use in all aspects of life, including international trade, manufacturing, security, health and safety, protection of the environment, and in the basic science that underpins all of these."

Can someone explain this to me, because I am so incredibly confused.

I commented about this in another thread, but I realize many people probably missed this and it’s not being talked about here, so I figured I’d bring it up.

The latest version of the SI Brochure, 9th edition V4.01, was issued this month. Its most significant change is that the category “Non-SI units accepted for use with the SI” was abolished. Table 8 has been repurposed into a more general non-exhaustive list of common “non-SI units”. I’ll transcribe the section below:

Non-SI Units

It is recognized that some non-SI units are widely used and that this is expected to continue for many years. It is therefore important to recall the values of these non-SI units in terms of SI units, because the SI is the internationally agreed reference with respect to which all other units are defined. A non-exhaustive list of non-SI units is given in Table 8, grouped into indicative unit categories to aid explanation.

Table 8. Non-SI units

Long-standing units of time and angle

• 1 minute (min) = 60 s
• 1 hour (h) = 3600 s
• 1 day (d) = 86 400 s
• 1 degree (°) = (π/180) rad
• 1 minute (′) = (π/10 800) rad
• 1 second (″) = (π/648 000) rad

Historical names for decimal multiples and submultiples of SI units

• 1 are (a) = 1 dam²
• 1 hectare (ha) = 1 hm²
• 1 barn (b) = 100 fm²
• 1 litre (l, L) = 1 dm³
• 1 tonne (t) = 1 Mg
• 1 angstrom (Å) = 0.1 nm
• 1 gal (Gal) = 1 cm/s²
• 1 bar (bar) = 0.1 MPa

Internationally recognised units that are not decimal multiples or submultiples of SI units

• 1 dalton (Da) = 1.660 539 068 92(52) × 10⁻²⁷ kg
• 1 astronomical unit (au) = 149 597 870 700 m
• 1 nautical mile = 1852 m
• 1 knot = (1852/3600) m/s
• 1 electronvolt (eV) = 1.602 176 634 × 10⁻¹⁹ J

Units used in specialized technical disciplines

• neper (Np)
• bel (B)
• decibel (dB)
• 1 var (var) = 1 W

(NOTE: No unit symbol is defined for the nautical mile or knot. In the 8th edition of the brochure, these units were respectively given the symbols M and kn, with the caveat that these symbols had not been internationally accepted. They are no longer recognized.)

The full version of the SI Brochure (9th edition V4.01) can be found here: https://www.bipm.org/documents/20126/41483022/SI-Brochure-9-EN.pdf/2d2b50bf-f2b4-9661-f402-5f9d66e4b507?version=7.0&t=1780410776583&download=true

EDIT: A post on the BIPM website dated 4 June 2026 clarifies the reasons for the change: https://www.bipm.org/en/-/2026-06-04-updated-si-brochure-clarifies-the-status-of-non-si-units

From that post: “The revised section on non-SI units responds to feedback received from stakeholders and clarifies how non-SI units are presented within the SI Brochure.

“For the first time since the SI was formalized, the SI Brochure now makes explicit that non-SI units do not hold any special status within the SI. The revision also introduces a more inclusive list of non-SI units together with their conversion coefficients to SI units.”

Recent threads have questioned the need for various units classified as "non-SI units accepted for use with the SI," and placed in Table 8 of the SI Brochure, with widely varied opinions ranging from love to acceptance to hate. The logarithmic units decibel (dB), bel (B), and neper (Np) are placed in this table. The decibel is widely used in electrical engineering, acoustics, communication theory, etc, and I think needs to be kept. I have never used the bel or neper or seen them used. Does anybody actually use them? Is there any need for them to be retained in Table 8?

The decibel could be retained and the bel dropped, similar to the hectare and are. The neper could be dropped if no scientific field uses it over the decibel (It can be expressed in decibels by a change of logarithm base). They seem unnecessary but opinions defending them are welcome too.

(As an electrical engineer who worked mostly in acoustics, you will have to snatch the decibel from my cold, dead hands.)