Consistency is not the only value of a system of units. Convenience is also of importance. And that is where the metric system shines. Having all measures of a unit in multiples 10 combines perfectly with our decimal calculations. Having as few as possible magical numbers to convert and combine between units makes making mistakes harder. How many calories in kinetic energy has a pound going 10 miles per hour ? I know a kilo going 10 meters per second has 50 joules of kinetic energy without looking up anything and doing the calculation in my head.
Can’t talk to the statute mile, but the nautical mile is sublime: one minute of latitude. The amount of math you can do in your head with a system with so many factors of 2, 3, and 5 is truly amazing.
Yes, meridians (on which latitude is measured) being a special case of great circle routes that happen to pass through the poles. That said, as a practical matter, you are more frequently contemplating a chart of smaller scale than "globe" so you're usually counting up distance between fixes, or distance to next turn in a harbor, or some such thing, where you have a compass in hand and just need to set the compass to the length of a mile. The nearest latitude tick marks are quite handy for that.
I'm not aware of any tricks to make mile calculations easier but the fractional scale common with the inch is very useful for real-world mental calculation and practical exchange. Effectively everything is powers of two. Got something between 1/4 and 1/2 inch? Great, use 1/8ths. It's three. Not close enough? How about five 16ths? It infinitely scales to provide another unit that is suited to the measurement at hand. In some contexts you might just say you pick the closest 1/8th. In others you might use 32nds. You can use the same measuring devices to agree on an ad-hoc standard that everyone understands.
But with the metric system you only really get cm (too coarse) and mm (too fine) but you don't get something like 9/16 so you can't "work in 16ths" and have everything be whole units again.
Adjusting HVAC in degrees-C is infuriating to my Fahrenheit sensibilities. 20C is cold, 22C is hot. 21C is probably ok but really I want something like 20.5C. The comfortable range for a room is 3-5 whole units of F, but requires a bunch of fractions in C that you may not even have available on your thermostat.
Sure, converting between units is easy in the metric system. That doesn't make it the best thing to use all the time. Hell, the idea of thousandths of an inch is used commonly, so even the imperial system is base 1000 in some cases. But I've never seen anyone utilize the fractional scale with metric units, probably because the units are the wrong size for that to be useful.
But with the metric system you only really get cm (too coarse) and mm (too fine) but you don't get something like 9/16 so you can't "work in 16ths" and have everything be whole units again.
People who use metric units are perfectly happy rounding to the nearest 0.5cm or 0.25cm if that's what's needed, exactly as people do with inches. Why on earth would you imagine people use mm if something doesn't call for them?
But does anyone say 1/8th centimeter? Seems easier to just drop down to millimeters at that point. Which is fine, but it loses out on the convenience of fractions.
As an occasional woodworker and carpenter, I can tell you having evenly divisable (inch) measurements makes mental division a whole lot easier. It's just a case of using the right tool for the job.
My argument is a mm is too fine in that situation. 1/8ths and 1/16ths are ideal when working at those scales.
In reality I use both systems all the time. It’s situational.
> When I hear anything past about 1/8th of an inch my brain shuts down, and I give up.
Realistically, same. 32nds don’t get used outside of some specialty wrenches. 16ths are a practical limit where other scales start to make more sense. Probably millimeters.
So 3 mm is a weird measure but 1/8 of an inch is just perfect? You are like those guys who say that Fahrenheit is better because it feels "more natural and obvious"
I don’t understand why it has to be one or the other? Working in fractions is nice sometimes. Inches are a useful size for some situations. I find it easier to say that’s three eighths than 9mm because my ruler doesn’t have different marks for the factors of each mm mark.
I use both systems.
I do prefer Fahrenheit for HVAC (and weather) because it’s higher resolution and has reasonable values at human scales. Thermostats that lack half-degrees-c are never quite right IMO.
> I do prefer Fahrenheit for HVAC (and weather) because it’s higher resolution and has reasonable values at human scales.
So you are one of those, lol. There is nothing "less human" about 25 C than say 72 F. Nothing, it just happen to be the scale you are used to.Both are arbitrary.
> Fahrenheit for HVAC (and weather) because it’s higher resolution
99.99% of thermostats and thermometer in C had at least 1 decimal place. At usual "human temperatures" the difference in resolution between the scales is less than 2X, so even assuming only integer values, I am willing to bet against you in a double blind test that you cannot differentiate 68F vs 69F in an statistical significant way.
> I find it easier to say that’s three eighths than 9mm
Just because you are used to. Fractions are more complicated than integers, every elementary school program knows it.
So to summarize, the problem is not with the magnitude of the units which is arbitrary (a degree F and inches are not more human, logical or normal that a degree C or cm)the problem is with the convoluted way of the imperial system for multiples and submultiples of the base unit.
“Human scales” meaning temperatures that won’t burn my skin or give me frostbite. 70 is nice. 60 is cool. 50 is cold. 40 is really cold. 80 is hot. 90 is really hot. 100 is potentially dangerously hot.
I guess 20.5 is nice, 15.5 is cool, 10 is cold, 4.5 is really cold, 26.5 is hot, 32 is really hot and 37.7 is dangerously hot. It’s fine if you are used to it but I don’t really see a benefit.
I was in a hotel room in Japan that only had whole unit adjustments for the A/C. To get 20.5C I had to switch to Fahrenheit. I guess I was unlucky.
I find distances in metric and imperial perfectly usable and use both regularly.
As outlined in detail elsewhere in the thread there are advantages to working in fractions in some situations. Specifically when using a ruler or tape measure with different markings for 1/2, 1/4, 1/8 and 1/16. There’s no reason that has to be unique to inches, it just works out well in some cases.
Sure, you can pick even numbers in either scale that are awkward decimals in the other. I just prefer the ten degree bands of the Fahrenheit scale for these ranges.
It's not really identical though. Like I said, Fahrenheit is higher resolution at these scales so that is an advantage. It doesn't mean everyone should convert to F. Just that both systems have benefits. If I changed my perception of the world to C I wouldn't actually gain anything, personally, in the context of weather and HVAC.
If I need to take measurements while boiling water or making ice then I would probably use C.
Interesting comment on Fahrenheit, as I would say it has too much resolution for day to day use. A nice sunny day is in "the low 70s". A cold winter day is in "the high 20s". There is too much precision in the units to give an exact numeric value, so we round it to low/mid/high. That implies that the general unit we should be using is somewhere around 3 times larger than Fahrenheit degrees, because that is the size of the unit we use in speech anyways.
People often say something is 1 and a half meters long. I don't understand how people can work with inch measurements. How do you divide 7"3/8 by 5? This seems a major pain.
There's something just right about 1/16th of an inch. About the same as a millimeter, and easy to do math with... it is weird though 1/8th, centimeter is hard to conceive, for me anyway.
When more precision is needed, so easy to go to the 32nd
All you're saying is that inches are what you're used to. Being in the UK I am familiar with both inches and mm, and mm are far easier to work with than 16ths of an inch.
If working with simple units of ten is beneficial then every mission should redefine units in terms of expected velocities and vehicle size so they are optimized for the actual calculations at hand.
That's not realistic, obviously, so we just pick one. The units in the system are arbitrary, really.
In reality regardless of the system you choose every calculation is going to end up with fractions of something. You aren't just going to do it in your head.
For example, you could define mars units where the gravitational acceleration on mars is 1. Now your velocity in freefall is just equal to the time you've been freefalling! You don't even have to do a calculation!
(note: Don't actually do this. Gravitational acceleration isn't a constant when you're doing orbital mechanics.)
Honestly I would expect something like that to be happening at a hardware level. The number of bits in a memory address for the ground sensing radar is very interesting. Or the algorithm to determine vehicle acceleration given the voltage reading of a solid-state sensor vs the baseline. The metric system vs the imperial system is not an interesting distinction in these contexts.
The main convenience of it is when deriving formulas, rather than when applying them. With all the constants set to 1, they don't need to be tracked throughout the formula, and can be put back in at the very end by looking at the units. Sprinkle the appropriate (hbar*c) or (mu0*epsilon0) at the end, and then you get your constants back.
