So when you give someone an inch, you're specifically giving 25.4mm ;)
[1] https://www.nist.gov/pml/weights-and-measures/si-units-lengt...
[2] https://www.nist.gov/sites/default/files/documents/pml/wmd/m...
And yeah. I mean 10 is only divisible by 2 and 5 where 12 is much more flexible in giving us 2, 3, 4, and 6. At least that was my grandfather's argument.
I annoying need to keep Metric and Standard wrenches and such for working on various things. Eventually it won't matter as the US will mostly source parts built over-seas where it will only make sense to adopt metric. And then the Standard system will only be left on road signs and temeratures, oh that's pretty much already happened.
Now that is some good ole American ingenuity :)
My "favorite" is "Well farenheit just makes more sense for humans".
I rely on unit tests for this stuff these days ;)
28 day months make far more sense, would align nicely with your proposed single New Year's day, and have the added bonus of aligning with our 7-day week system quite nicely. This ends up with 13 months altogether, and hey, it turns out that 28 days is closer to a lunar cycle, so the full moon would end up happening at roughly the same time every month. Not perfectly of course, but with the chaos that is our solar system, I'll take what I can get. https://en.wikipedia.org/wiki/International_Fixed_Calendar