In a world with only light cars you use a tax system that makes sense in a world with only light cars. In a world with cars that do significantly more damage, you should not as it is NOT THE SAME WORLD.

An not-really-that-efficient sedan certainly will not do better with a bigger box on top...

There certainly are thirds, even if they are expressed in scalable percentages.

There are 33%, 66% and 67% percents, but as repeatedly stated decimals just don't divide into thirds cleanly, there are no thirds in the 3 feet to a yard sense. Point being that even division just isn't that important.

It doesn't come up as much in daily life..

I suspect what "comes up" and doesn't is quite dependent on what is easy to do. I find myself calculating the volume of containers quite often, it is very handy when adjusting volumetric yield sizes to pans/containers. I could measure the capacity by pouring water of course, but why mess around with that if your measuring system has the tools built in? I was not very pleased when trying to figure out how many cubic feet of soil it would take to fill up a tote with the volume given in gallons. Neither are the units related, nor is it easy to convert between cubic inches to cubic feet (unless you are well versed in cubic duodecimal calculations).

The thing about the customary measures is that they evolved with the uses they are put to. They are the result of what people found most useful rather than what was prescribed.

That's not really a fair description. Considering the plethora of contradictory standardized and customary units that were floating around before metric alone makes it questionable. The fact that many contradictory versions of the "same" units were in fact mandated at various times and places outright contradicts such a claim. I'd say it's more fair that customary measures are units that some people, at some point, found useful for their particular tasks and were subsequently adopted for broad usage via network effects.

That's the reason I keep beating the "arbitrarily precision" drum. When you have a system where conversions are easy, you can adopt whatever approximations are useful for the task, instead of dealing with someone else's foot or stride you can have yours and retain all the advantages of a cohesive measurement system with a few basic calculations. If the size of the standard 12 inch foot makes sense for your task and clean division by three is important, then there's nothing wrong with working in 30 cm increments (or 3 dm, if the task scales up more than down).

It is a useful intellectual exercise to consider a metric system not based on ten though. It would retain the natural cohesion between length and volume (and mass for for water). but might use halves and thirds rather than tenths.

Oh, absolutely, however I'd go for an all out base 16 change across the board. As I said, for practical purposes (1) approximations of repeating numbers are adequate as long as the system easily supports arbitrary precision, (2) there will be repeating numbers no matter what, (3) binary divisions are the only inches easily eyeballed and performed without a lot of fuss and/or special equipment. For example, high precision division of weight is very easy in a base 16 measurement system, whereas any base divisble by three is as problematic as decimal.

I'd imagine for that purpose 21 x 30 cm would be precise enough and the same number of digits. Not that I've ever had trouble remembering the extra 7... Of course I'm a nerd who knows that sqrt(2) is approximately 1.414 and can get there from 21 cm. Of course I know that precisely because I find the A series so cool.

Sounds like rounding to millimeters would be plenty accurate then.

There are no thirds in serious baking, it's all decimal in the form of baker's percentages that can be used with whatever weight units you want.

I'll note that it would probably reduce headaches quite a bit if the foot was removed from the yard/foot/inch equation, as it stands 3 parts is the only thing the yards divides evenly to for the next smallest unit. I'd rather deal straight with 36 inches, of course most people have decided to go the other way and ignore yards when inches are in use.

Overall yards are a prime example of the problems with US customary units: inconsistent divisions. Commonly used lengths go from 1760 to 3 to 12 to binary division (so there are common factors, but the bases don't normalize until you divide inches), and miles are usually given in feet, not yards to top it off. Plus I believe there are random sub-inch units, but I don't know how they fit, or don't fit into this "framework".

Then there's the lack of cohesion with dimensions and volume/weight disconnected. Volumes are at least mostly (ah, teaspoons) consistent with a binary division, however the individual divisions have names, half of which have been forgotten. So people learn seemingly arbitrary conversion factors between ounces and cups and quarts and gallons without knowing the underlaying system.

Err... disregard those numbers, I had a brainfart. Point is 11x17 has a completely different aspect ratio (1.5454...) than 11x8.5 (1.2941...) meaning that while it has twice the surface area it is useless for printing things designed for Letter besides printing two copies on one sheet. A3 is twice the size of A4 in area while retaining the aspect ratio.

I'm not entirely sure which point this answers, unless there is a common 16.5 x 10.5 paper format out there or somesuch.

A cup is a cup... except when you try to cut a recipe calling for a third cup in half. Stop obsessing over precision if all you care for is approximates. Also, once you've nailed grandma's bread recipe, recording to the nearest 5g-10g will really help you repeat it.

Anyone who cares will know that it's one newton per square meter, which has the advantage of avoiding the ambiguity of "pound". As for chunkiness, pick whatever estimation unit you are comfortable with, if increments of 4 liters make sense to you then do that, you'll still have liters in the end. I personally calibrate my volume and weight estimation with soda bottles, I just can't easily feel a single kilogram with the same precision, much less a pound. Two kilos is just right however.

Not to mention dimensions into volume. A 4' x 2' x 2' container holds fuck-you gallons of water.

768 teaspoons... that are then divided by two again. What's not to love?

The reason no one converts between feet and miles is because it's a pain in the ass, this doesn't prove it's not useful.

Your circular handsaw still has the same precision... If you are close enough to 1/16th of an inch when cutting to millimeters, you won't know the difference between having done it in 1/16th. I also think that European construction workers would disagree on the usefulness of inches.

Those feet to inch conversions, works great if you leave them out. Now out of a sample of 10 random people how many can do this quicker in binary than decimal?

Except that every man uses base 10 for his calculations already, so familiarity will outweigh the meager "benefits" (because 1/3 will do when it really matters, that is, almost never). Not to mention that US customary only enjoys 12 at one step of the length unit continuum, negating the whole point by just being random. And if we disregard what base everyone is familiar with you'll find that humans can't actually divide by three without measuring tools, which means that it's 8 or 16 that make for a easily divisible base, not 12. 12 is great for selling integer goods, but it has no tangible benefits as a numeral base, particularly when point fractions are used.