Units of Measurement

psikeyhackr

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Kids are really funny. When I started reading SF the heroes were always 6 ft tall or more. I remember thinking, "I've got to be at least 6 ft tall when I grow up." That is probably why I am 6'1".
 

Lostinspace

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David Drake in the RCN series has one culture using Imperial and its opponent using metric just to show that these are two human cultures which recovered from a galactic collapse independently.
 

Harpo

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Here is a simple guide

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Ambrose

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I seem to remember it being said that when one Mars probe disappeared when close to Mars that a course correction burn was calculated in imperial but made in metric, or vice versa.
 

Christine Wheelwright

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Its ok ordering a beer or buying tomatoes, but nobody should be doing any proper science or engineering using anything other than SI units. And that is certainly the case in most countries including the UK. It is only in the US, where a strange 'small c' conservatism prevails, that scientists and engineers persist with these nonsensical units. Basically the same reason the $1 bill wasn't replaced with a coin decades ago.
 

Swank

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Why are writers putting the measurements of stuff in stories? How super uninteresting and pointlessly technical.
 

farntfar

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You have to be able to quantise stuff even if it's only in made up units.
"The beast must have been 57 swaddoodles tall if it was a mulch."

The base was 7 garkons away and my arcturian ultrahorse could only run at 35 yarps per jankle. I was never going to make it in time.

Otherwise you just say
"The beast was big"
and
"My top speed was insufficient for me to make it in time"
Less technical but also less interesting in my opinion.
 

Pyan

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When Gerald Durrell, the naturalist and author of “My Family and Other Animals” was collecting animals for zoos in the 60s in West Africa, he used to hire locals to carry the expedition equipment into the bush. Apparently they used to measure distances by the time it took to smoke a cigarette, so if you asked them how far it was to, say, the next village they would tell you it was “three cigarettes away “.
 

Wayne Mack

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nobody should be doing any proper science or engineering using anything other than SI units.
Unless one considers lightyears. Trying to use a single measurement and scaling it up and down doesn't make sense as opposed to defining a measurement the fits the purpose. Also, base 10 is a pretty bad choice; There is a lot to be said for using base 12 for human operations and base 8 or 16 for computer-based. 1 hour is more understandable than 3.6 ksec.
 

Christine Wheelwright

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1 hour is more understandable than 3.6 ksec.

It is until you start doing science. F=ma is only true when force is in newtons, mass is in kg and acceleration is in m/s^2. You could try using other units (like hours and pounds) but then you would need to add a multiplier/constant from a dog-eared reference book that your colleague borrowed a month ago and never brought back. I've actually been in this situation (in the US of course....sigh) when a room full of mechanical engineers wanted to work out the torque of a machine when they knew its power (in hp) and speed (in rpm). A guy went off to find the book. Meanwhile I converted hp to W (which I just happened to recall is x 0.75 x 1,000) and converted rpm to radians per second (divide by 60 and multiply by 2xPi) so that I could get the answer in Nm (no looking up of constants). SI units for the win!
 
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Venusian Broon

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It is until you start doing science. F=ma is only true when force is in newtons, mass is in kg and acceleration is in m/s^2. You could try using other units (like hours and pounds) but then you would need to add a multiplier/constant from a dog-eared reference book that your colleague borrowed a month ago and never brought back. I've actually been in this situation (in the US of course....sigh) when a room full of mechanical engineers wanted to work out the torque of a machine when they knew its power (in hp) and speed (in rpm). A guy went off to find the book. Meanwhile I converted hp to W (which I just happened to recall is x 0.75 x 1,000) and converted rpm to radians per second (divide by 60 and multiply by 2xPi) so that I could get the answer in Nm (no looking up of constants). SI units for the win!

When you see some of the 'higher level' equations in non-SI units, it's enough to tear your eyeballs out. The basic form of the equation, of course, does not change, but there are some very odd constants required. Stick to SI and keep it there!


Unless one considers lightyears. Trying to use a single measurement and scaling it up and down doesn't make sense as opposed to defining a measurement the fits the purpose. Also, base 10 is a pretty bad choice; There is a lot to be said for using base 12 for human operations and base 8 or 16 for computer-based. 1 hour is more understandable than 3.6 ksec.

Hard disagree. Measurements that 'fit the purpose' just gives you a bunch of units with very odd conversions between all of them. Also base 10 a bad choice?!?! Poppycock! ;)
 

Wayne Mack

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It is until you start doing science. F=ma is only true when force is in newtons, mass is in kg and acceleration is in m/s^2. You could try using other units (like hours and pounds) but then you would need to add a multiplier/constant from a dog-eared reference book that your colleague borrowed a month ago and never brought back.
1 poundal = 1 lb * 1 ft/sec^^2
This requires a need to be looked up conversion factor of 0.138 to convert to Newtons.

The basic equations of physics do not require any specific arbitrary system of measurement to remain true. For human-based needs having units divisible by 1/2, 1/3, 1/4, and perhaps 1/5 is useful. For computer-based factors of 1/2 are more natural and base-10 math quickly begins to inject error.
 

Pyan

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Swank

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You have to be able to quantise stuff even if it's only in made up units.
"The beast must have been 57 swaddoodles tall if it was a mulch."

The base was 7 garkons away and my arcturian ultrahorse could only run at 35 yarps per jankle. I was never going to make it in time.

Otherwise you just say
"The beast was big"
and
"My top speed was insufficient for me to make it in time"
Less technical but also less interesting in my opinion.
Those are examples of frankly bad writing.


The units of measure that matter in fiction are the ones that relate directly to the scale or events of the characters.

It was horse-like, but he couldn't even see over the beast's shoulder.

She watched as the time counted down faster than the than their track on the Nav. They weren't going to make it.


Jargony units and the suggestion that the reader can do the math along with the characters is exactly the kind of thing that gives genre fiction such a bad reputation.

Whenever you feel the need to include a bunch of numeric exposition, re-watch the Monty Python skit about a murder mystery based around train schedules.

Or watch yet another hoary STNG episode where the 'acton' involves relentless discussion of phase modulation.

Then write something that personalizes the events to the characters.
 

Ursa major

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Then write something that personalizes the events to the characters.
There can't be many people who know no units at all, or do but can't put numbers to them, if only to evaluate things like periods of time and prices.

I suppose one could (in fantasy) invent a society that had no units, or a story so short that no units of measurement were made, but I suspect it would be half-cheating if everything was "measured" by comparison because, in effect, the size of one of the two things being compared would be, at that moment, a unit (in the way that a London bus, a football pitch and Wales can be units).
 

Swank

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There can't be many people who know no units at all, or do but can't put numbers to them, if only to evaluate things like periods of time and prices.

I suppose one could (in fantasy) invent a society that had no units, or a story so short that no units of measurement were made, but I suspect it would be half-cheating if everything was "measured" by comparison because, in effect, the size of one of the two things being compared would be, at that moment, a unit (in the way that a London bus, a football pitch and Wales can be units).
I didn't say there were people who don't use units. I'm saying that units of measure as descriptors make for fairly awful prose and have little connection to how impressed the characters are about that size, distance or amount of time. It isn't unrealistic for people to converse about numbers, just as it isn't unrealistic for people to talk about shopping lists and the neighbor's haircut.

But if you are writing something that is supposed to be entertaining, why include dry, lifeless data when you can suggest how that impressive thing feels rather than measures? What is the point of something being large if the characters or reader have no connection to it?
 

Wayne Mack

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Measurements that 'fit the purpose' just gives you a bunch of units with very odd conversions between all of them. Also base 10 a bad choice?!?!
Addressing the second point first. Try this. Draw a line across a piece of paper. Mark 1/10th of the line. Try again, but mark 1/2, 1/3, and 1/4. Now, draw a short line. Draw another line that is 2x, 3x, and 4x. Repeat and draw a line that is 10x. Unless I'm mistaken, one will find that factors of 2, 3, and 4 are readily visualized, while factors of 10 are not.

Now consider time. The relationship between common units is certainly not decimal. The units are chosen on the question that one wants answered.

The relationships between various imperial measures are typically ratios of 2, 3, and 4. Nothing too exotic. The imperial system provides a wealth of individual measures that are coupled to the scope of whatever is being measured and can easily be scaled upward and downward. The metric system, though, has a sparser set of measures (I will assert that adding prefixes, such as centi- or kilo-, creates a new unit of measure).

The conversion factors between imperial measures are not that complex and the quantity of measures allows selection of units appropriate to the question at hand. Conversion factors only become complex when trying to switch back and forth between imperial and metric.
 

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