Never heard of an acre-inch before, and I'd have to get out a calculator to work out how much water that actually is in pints or gallons, or how much it weighs.
The metric equivalent would be a hectare-meter or a hectare-mm. I know a hectare is 100 m x 100 m, so 10,000 m². So I instantly know that a hectare-meter is 10,000 m³ (10 ML, or 10,000 tonnes of fresh water). A hectare-mm is 10 m³ (10 kL). If my 1 ha block gets 1 mm of rain, then that's 10 kL or 10 tonnes of water. So easy i can do it in my head.
> And of course an inch is 2.4cm
2.54 cm.
The recommendation for emergency supplies is about a gallon of water per person per day - or 3.7 liters if you're using metric.
I've also heard it claimed that the 0-100 Fahrenheit scale is more functionally useful because the endpoints of 0 and 100 represent the tipping point of serious danger for humans from hot or cold weather. The closer you get to 100 degrees the more care you need to take about heat stroke and keeping hydrated, and similarly the closer you get to 0 degrees the more care you need to take about retaining heat and staying out of the elements - the freezing and boiling point of water isn't a necessary marker for survival. And people like nice round numbers to serve as markers for such things, divisibility be damned.
Metric is sterile and functional for calculation and consistency, which is fine and necessary for many things, but that's not a reason to completely ditch Imperial.
US customary is not "thousands" of years; temperature (Fahrenheit) only came out in 1724 for example, and many other units were only standardize much more recently:
* https://en.wikipedia.org/wiki/History_of_measurement#History...
* https://en.wikipedia.org/wiki/System_of_units_of_measurement...
Second, even with-in the system itself there was also sorts of inconsistencies. Until just a few years ago there were two "foot" units; one was recently retired:
* https://www.nist.gov/pml/us-surveyfoot
Here's another one: which weighs more, a pound of feathers or a pound of gold? A pound of feathers. Because feathers use one 'pound-system' [1] and is 453g, while gold uses another pound-system [2] and is 373g. But of course an "ounce" of gold (31g) is more than an "ounce" of feathers (28g), because Troy is 1/12 of pound but Avoirdupois is 1/16. In addition to the above "ounces" there is also "fluid ounces". And let's not forget about the third system [3], which got replaced by… the metric system in 1971.[4]
[1] https://en.wikipedia.org/wiki/Avoirdupois
[2] https://en.wikipedia.org/wiki/Troy_weight
[3] https://en.wikipedia.org/wiki/Apothecaries'_system
[4] https://en.wikipedia.org/wiki/United_States_Pharmacopeia
Also:
* https://en.wikipedia.org/wiki/Pound_(mass)
* https://en.wikipedia.org/wiki/Pound_(force)
> Think about it. Imagine you were never taught a measurement system. You find yourself needing to come up with a unit to make measurements for wooden planks you're going to use to build a house. Would you choose a unit as long as a meter? Or one as short as a centimeter or even a decimeter?
Millimeters. That single unit gets you down to very small scales (finer than 1/16") and to large lengths: four significant digits (9999mm) gets you to the equivalent of >32' (~11yd).
* https://web.archive.org/web/20200516223819/https://themetric...
As evidence for this Australia/NZ/EU do everything in millimetres in construction.
You misunderstood me. It's based on measurements that people have been using for thousands of years. The Romans had feet and miles, for example - not exactly the same lengths, but for the same purposes. The Japanese shaku is almost exactly the same as a US foot. A Japanese Shō is about half a gallon. A Chinese jīn is just slightly larger than a pound. There's a reason for this.
> there was also sorts of inconsistencies
I never claimed otherwise. But do notice that the survey foot and standard foot weren't used for the same purposes, and the difference between them wasn't likely to confuse anyone except maybe people new to the field.
> Here's another one: which weighs more, a pound of feathers or a pound of gold?
Yep, Troy weights. And no one's sure where the Troy system came from. The main reason for its use is because of international trade. Also not something regular people (i.e. people that didn't work directly with precious metals) would have had contact with.
> Millimeters
Hah! Yeah right. Look at all the various non-metric systems that have existed throughout history. Did any of them use something like millimeters to measure wooden planks? Why not?
> As evidence for this Australia/NZ/EU do everything in millimetres in construction.
They do it because the metric system is mandated there and it doesn't give you reasonably sized unit for that scale of work.
Try this: go to a home center (or whatever it's called there - the place you buy building supplies) and measure some drywall. Do the measurements you made agree to the advertised ones within half a millimeter? Compare the dimensions of drywall sheets from different pallets and manufacturers. Do their dimensions agree to within half a millimeter? If not, that's a sure sign you're using units poorly adapted for purpose.