You shouldn't use degrees for Kelvin, it's an absolute unit, the degrees are needed for the relative units like Celsius.

Anyway, the French system isn't what people mean by "metric" in this context, they mean the SI system of units, and so in practice it's not so much that it wouldn't matter which you choose as that you don't have any option except SI.

If you wanted an independent system of units you'd need to do a lot of expensive metrication, and in practice Americans are too cheap for that, so the US "customary" units are just aliases for so-and-so-much amount of some SI unit, they aren't actually independent at all.

The reason people focus on metric is that for everyday people that's the part which jumps out as more intuitive. All these nice powers of 10, very tidy.

It's useful in STEM because SI units are often straightforwardly defined in terms of one another, it substantially reduces the amount of arbitrary constants you need in your equations, making them a lot easier to work with.

However the abbreviation is STEM. For S and especiually M you can do in different units.

For T&E it really matters see NASA's Mars Climate Orbiter and the need for heroics in the Gimli glider.

You need to keep to the same unit.

>Every single country in the world that is on metric today had to switch from something else at some point in the past. Why overfocus so much on UK when you have literally a hundred successful examples?

A huge percentage of those countries didn't have established industrial bases, infrastructure, etc. And also no educated general populace that needed reeducating. And often those countries were effectively forced into adopting metric through colonization and/or invasion.

The trouble is there is just very little gain. It really just doesn't matter. All the systems are fine, they all work. If you come live here, you'll adjust after 2 years. If I moved to Europe, I would adjust in 2 years. Once in a blue moon you have to bother with converting units but c'est la vie. There's bigger things to worry about.

>Other countries switched.

Except they didn't actually, see my points about the UK (similar points apply to Canada).

Distances in the UK are measured in miles and yards (or fractions of a mile). Google Maps gets this wrong and uses miles and feet. I don't think many people in the UK have a good intuition for how far 500ft is.

If you buy beer "loose" like at a bar it has to be sold in pints. Most people will have seen a "half" and anybody who likes stronger beers or goes to festivals where you taste different ones will know a "third" of a pint is also a legal amount of beer to sell. You would not want to try out a few different 8% stouts if they were sold only in whole pints, unless they're going to make it a multi-day event and provide somewhere for you to sleep it off.

Milk is also allowed to be sold in pints, traditionally glass bottle re-usable milk bottles were one pint.

It is also usual (but not legal) to sell a pint or a half of various soft drinks, in theory you should be sold these in some other way, I always say "large" or "small" but in practice ordinary people say "pint" and after all the staff will probably more or less fill a pint glass so, whatever.

Spirits (e.g. gin) are measured in either 25ml or 35ml shots. An establishment can choose either, post which one they picked and use that consistently. Why two seemingly unrelated sizes? Well, historically there were two different non-metric sizes permitted in law, and when the government legislated to make these SI units there were lobbyists demanding they allow this to continue despite the opportunity to rationalize.

As in the US, containers you purchase in a store are labelled, but here the labels must prominently show SI volume units and EU-style value metrics are required on shelf markings, so e.g. 10p per 100ml of Coke is a good price, maybe the Pepsi is on a deal for 9.5p per 100ml, the store's terrible own brand is 5p per 100ml. This EU strategy prevents people screwing with sizes to make you think you're getting a better deal, that cheaper bottle may look like a good idea but hey, it's 18p per 100ml, ah, it's slimmer in the middle which makes it actually much smaller than it looks.

Yes, so you have all the disadvantages and none of the advantages.

And sure, of course metric isn't necessary. You can also write all software in COBOL and PL/I. But over the long term, the convenience of having a self-consistent system based on a few simple principles rather than historical precedent adds up.

> Legal size folders exist and are widely used by people who use ... legal size paper.

Sure. But I didn't know I use legal size paper or even what it is before I asked the apartment complex to print the lease agreement, and it didn't fit in their own folder with the other move in papers. In my rank of weirdness discovered upon moving to the US, this is at about the same level as the different ounces.

I'm just about old enough to remember (in the UK) foolscap paper, an imperial size also a bit longer than A4. You never see it any more (at least I don't) but foolscap sized box-files are still readily available. I guess a slightly bigger box than you need is not usually a problem.

Many filing cabinets in the US are also sized so you can put letter sized folders in one way, or rotate the folders 90 degrees and legal sized folders will fit correctly.

> It just doesn’t matter in daily life.

Like a lot of mathematics it does matter in your daily life but you actually just don't think about it because of course this works - unless you're an American and so no it doesn't.

The A-series paper sizes mean everything scales very naturally. Poster? Pamphlet? It's just the same ratios again but bigger or smaller. There is a single design where this works, and that's why the A-series exists, you can't just pick anything, only this works.

For a normal letter, it probably doesn’t matter. But it’s useful in general and doesn’t make it worse for writing letters, so it’s still better to use than a specific letter format with worse properties.

> Right, but why does that make letter size confusing?

That's the part I initially quoted; "the paper that the text was printed on wasn’t an A4, it was smaller and not a size I was familiar with. I measured it and found that it’s a US letter size paper at about 21.5cm x 27.9cm"

The author isn't from North America, so they had forgotten the format was different, so they got confused when they assumed it would have been A4 like the rest of the world, but it wasn't.

> the only people in the US who would even notice would be people who commonly do business with other countries or who live near the border

Or, as in the case of the author, they live outside of North American and send/receive letters to/from North America.

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Well, "A4" doesn't imply anything about the intended use. The format of the name also implies that there is A3, A5 etc, both of which aren't all that uncommon either.

But, yes, for most people it doesn't really matter - you go to the store, you buy paper, you shove it into your printer, and it mostly just works. However, it's also not all that hard to run into situations where things break. E.g. most PDFs originating from US are rendered for Letter size paper, which means that printing them outside of US generally requires setting "fit size" rather than "original" to ensure that nothing gets clipped. Vice versa also happens, but because US is so culturally dominant, Americans rarely run into that particular issue.

Yes, but that’s the annoying part. So many tech problems that people encounter can be trivially solved with a quick web search, poking at menus until you find something promising, or a combination thereof. I remember helping my mom over the phone to troubleshoot something on her iPhone – at the time, I had an Android, so everything was foreign to me, but I was able to deduce where a given setting might exist, and figured out whatever the problem was.

I don’t know when or why this skill declined, but it’s upsetting.