What can I do with these rulers?

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MetricRocketeer

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It's not complicated, it's just different.
Hi @lakeroadster,

I disagree. It is complicated.

76 metres is, to the nearest whole number, 249 feet. Divide 249 by 1000 and you get 0.249. Now you have to convert 0.249 feet into inches, but using the metric system you don't have to do any conversion.

Stanley
 
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Blast it Tom!

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I mentioned elsewhere that, when they figured out that a meter wasn't 1/10,000,000 of the distance from the equator to the pole that James Watt proposed they make a standard meter such that 40 inches would equal one meter. That makes a lot of sense to me, then 1 inch is 2.5 cm, and such. But for whatever reason, they stuck with what they had.
 

lakeroadster

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Hi @lakeroadster,

I disagree. It is complicated.

72 metres is, to the nearest whole number, 249 feet. Divide 249 by 1000 and you get 0.249. Now you have to convert 0.249 feet into inches, but using the metric system you don't have to do any conversion.

Stanley
Opinions vary. I've used Imperial Units for over 5 decades, it's not complicated to me, more like just another day in paradise.

Your "username", your "custom title" and previous posts here on TRF about this very same topic, indicates this is a topic you are passionate about.

I doubt you'll convince anybody here to buy a soapbox 🧼📦 and join you on your crusade.
 

mh9162013

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It is complicated.
Sometimes it is, especially when converting.

But depending on what I'm working on, it's much easier to deal with whole numbers and basic fractions than decimals.

If I had to choose just one system to use, I'd choose metric. But b/c I can use both, metric isn't always the system I use.
 

MetricRocketeer

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But depending on what I'm working on, it's much easier to deal with whole numbers and basic fractions than decimals.

If I had to choose just one system to use, I'd choose metric. But b/c I can use both, metric isn't always the system I use.

Hi @mh9162013,

When, may I ask, is it easier to deal with fractions than decimals?

Stanley
 

mh9162013

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Hi @mh9162013,

When, may I ask, is it easier to deal with fractions than decimals?

Stanley

It's usually when I'm measuring something and I need to scale it up or down.

For example, if I wanted to downscale a model submarine by 1/2 and the hull is exactly 4 and 1/2 inches in diameter, it's much easier to cut 4 and 1/2 inches in half than it is to cut a 11.43cm (or 114.3mm) in half.

But it also works the other way. If I need to calculate the size of my ballast tank which is going to be somewhere between 300 and 400 ml in volume, it's a lot easier to work in ml or cc than it is in cups, where adjustments to the ballast tank size likely be in 10ml or 50ml increments. See, these are whole numbers that are easier to work with than 1/4, 1/8, 5/16 cups, etc. Or heaven forbid, tablespoons and teaspoons.

In the rocket context, a good example is with fin thickness. 2, 2.5, 3, 3.5, 4mm, etc. is a lot easier to work with than 1/8, 3/16, 5/32 and so on (yuck).
 

MetricRocketeer

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When the kit you are building has dimensions in Imperial units, and you have a scale layed out in Imperial Units.
Hi @lakeroadster,

Right. But that's the point. If we used the metric system, then kits would never be laid out using foot-pound measurements. Kits would be laid out only in metric units.

Stanley
 

MetricRocketeer

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Might be a good idea to put Maryland in your profile.

Born and raised there?

Do you work at a facility that only uses metric?
I will edit my profile. Good idea.

I teach mathematics, and it pains me to see students have a disadvantage right out of the starting box having to grapple with an archaic, inefficient measurement system just to measure the distance from Point A to Point B.
 

KC3KNM

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I will edit my profile. Good idea.

I teach mathematics, and it pains me to see students have a disadvantage right out of the starting box having to grapple with an archaic, inefficient measurement system just to measure the distance from Point A to Point B.
I'm not sure what the polices are like at your district, but I grew up learning both systems congruently and I think that's been really valuable in my professional life. Having grown up in the US (and in a machine shop) I'm much more comfortable working in inch, but I work in both systems every day. I commonly receive prints that have both imperial and metric measurements in them. Seeing as the world is still hanging on to a lot of imperial measurements, even outside the US, having an understanding of both is pretty important IMO.

FWIW we had a pretty large section on the metric system and units when I went through tech school in the AF. Even our military is aware of the value of it's members being familiar with the metric system, but we're not quite ready to drop the inch. Not sure when that would make sense, but I don't think the current state of measurement in this country is some inch driven hellscape.
 

MetricRocketeer

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I teach at Towson University.

I stay on topic, and from time to time and only briefly I say a few words promoting the metric system.

However, since teaching materials often refer to measurements using the foot-pound system, I have to show calculations using the foot-pound system. And that's the problem. Instead of being able to concentrate on the mathematics of the situation, I have to get distracted navigating the inefficiencies inherent in the foot-pound system.
 
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Sandy H.

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Hi @lakeroadster,

Right. But that's the point. If we used the metric system, then kits would never be laid out using foot-pound measurements. Kits would be laid out only in metric units.

Stanley

I agree, but that is an unfortunate perspective, IMO. It is ideal to be fluent in everything you're going to deal with and for people in the US, that means the imperial system and also the metric system. The history of units is interesting (a long time ago, I watched a Youtube video talking about the various ways that units would change from king to king and that made a complete mess in Europe!). In a perfect world, we would all use the same unit system and I personally wouldn't necessarily care what it was based on - if it was uniform, then it is the most easy.

The counterpoint to that is that if we all spoke the same language, then things would be easier. Given how humanity has evolved, however, I think it would be a real tragedy if we all did speak the same language. The amount of culture and history contained in language is hugely important. Additionally, you may or may not agree that people who are fluently multi-lingual likely have an advantage over people who are mono-lingual in many circumstances. I believe, but don't know (and don't feel like researching it at the moment as dinner is almost ready!!!) that people who are multi-lingual tend to have very good cognitive skills compared to others.

Mathematically, I am sure that my mind is more agile due to the ability to work in imperial units (decimal or fraction), metric units, hexadecimal and binary (in that order of my fluency). Each base has its place. Mastering all of them will simply make you better equipped to handle any situation you come across. If you never come across those situations, then the advantage is minimal, but if you do, you leap ahead of others. To me, ensuring university students in engineering or science related fields should require mastery of various units and bases, as that stretches the brain and helps quick analysis of situations.

All of the above is just my opinion, but I feel knowledge is power and knowledge of fractions is something everyone should have, metric or imperial.

Sandy.
 

bjphoenix

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Have y'all seen these type rulers?
They have .5mm pencil slots for marking stuff; search, there's a bunch of different ones.
I've seen them, they're primarily intended for woodworking and there are a number of companies making them in different styles. They function like a T-square where you put the side against the side of your piece of wood, put your pencil in the chosen slot, and slide the thing down the edge of your piece drawing a line parallel to the edge of the piece at the chosen offset. I'm not real sure how they could be used for rocketry unless you used them for drawing parallel lines in conjunction with a drafting board.
 

bjphoenix

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Hi @bjphoenix,

We are not disagreeing, are we?

Let's say that a real-life rocket has a length of, oh say, 76 metres. If you want a one-thousandth scale drawing, then the size of the rocket would be 7.6 centimetres, or 76 millimetres. Using the foot-pound system, the calculations would be much more complicated.

Stanley
The architects scale a scale at one extreme intended to scale something down so that 3/32" on paper equals 1' in the rel object, this is used for drawing things like floor plans. The actual scale would be 128:1. At the other extreme the architects scale has a scale intended for 3" on paper equals 1' in the real object. This is intended to draw enlargments to show how small parts fit together, and represents an actual scale of 4:1. If you had a rocket with dimensions given in feet and inches and you wanted to scale it down by one of these scale factors, the architects scale could be used, but it would be somewhat limiting because you would have to match one of these somewhat odd scales and the original dimensions would have to be given in feet and inches. For the architects scale I have on my desk the scales would be 128:1, 96:1, 64:1, 48:1, 32:1, 24:1, 16:1, 12:1, 8:1, 4:1. These scales are used frequently in my business, at least when we work with drawings on paper.

The engineers scale on the other hand is intended for even smaller scale things like the plan of a whole neighborhood. Its scales are supposed to be used such that 1" on paper = 10' of the real thing, 1" on paper = 20' of the real thing, etc. Note that it has nothing to do with feet and inches, it works with decimal numbers only. However the scales can also be used to scale something down by 1/2, 1/3, 1/4, 1/5 and 1/6, so it could be used with rocketry assuming you have the original measurements in decimal inches. (I have a Peter Alway book with measurements in decimal inches.) If you use the scale the way it was intended to be used it would scale things down very much further, 1" = 10' for instance is a scale factor of 120, and 1"=60' is a scale factor of 720. I have one of these scales on my desk too but it doesn't get used very much in my business. I find that when I'm scaling things I end up with weird scale factors so I might not ever get to use this scale for that.

The last scale model I worked on was an AerobeeHi. In Peter Alway's book the airframe is 15.0 inch diameter, I was scaling it down to BT-60 size so that meant a scale factor of 9.15:1. I just drew it up in Autocad using the measurements in the book, then scaled that drawing down by this scale factor. Then I could measure all of the dimensions I needed from the reduced drawing.
 

MetricRocketeer

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I mentioned elsewhere that, when they figured out that a meter wasn't 1/10,000,000 of the distance from the equator to the pole that James Watt proposed they make a standard meter such that 40 inches would equal one meter. That makes a lot of sense to me, then 1 inch is 2.5 cm, and such. But for whatever reason, they stuck with what they had.
Hi @Blast it Tom!,

Actually, I didn't know that about James Watt. Could you kindly provide some background or more information. Do you know what year he said this? Do you have a quote from him on this topic? I am really curious.

Thank you.

Stanley
 

smstachwick

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In response to the general trend of users twisting their heads around about units, I emphasize this most heavily: use what is most familiar and comfortable for a given application. For me, motor diameter (and frequently, length) is in millimeters, altitude is in feet. Acceleration is in g, liftoff and propellant mass are in grams (g). Rod clearance speeds are in mph, airspeed is in mph or Mach. Descent rate and touchdown speed in fps.

Also be OK with approximating conversion factors and measurements when appropriate. About 25mm to an inch, about 30cm to a foot, a little over 3 ft to a meter. A meter stick comes up to about my hip, the tip segment of my thumb is probably just shy of an inch, and I can measure out about a foot by tucking my elbows into the thin part of my abdomen and sticking my fingers out directly in front of me. A gram is about the mass of a paper clip. Average speed over uneven ground, barring injury, is 4mph.

These estimations will be less useful in detailed scale work and engineering, but for the lazy sobs throwing together random crap at the range itself with the goal of producing a flyable rocket using a minimum of measurements or dimensional data, they’ll be invaluable.
 

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I see. I feel compelled to ask: Do you attempt to groom your students into using the metric system, or do you stay on topic and teach the curriculum that
you have been assigned to teach?
That's a ... rather loaded way to ask the question.

But back to the topic at hand, architect's scales are really useful if you have scale drawings and are trying to measure things that aren't dimensioned for a scale model. I used to have a full architect's (US unit) triangular scale like those plus a metric one with lots of popular scales, but now I just use a small two-sided one as most of our drawings are PDFs now rather than on paper. I do find myself scaling off of scanned drawings on the screen, though.
 

Funkworks

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What I'd like to see is a ruler with very thin markings. Someone should research (or look up) just how thin a marking can be while staying visible. And figure out what colors are best for this purpose. Maybe flurescent, or even back-lighted.

While I'd like everything to be metric, the physicist's point of view is that when a conversion is linear, be grateful, it's simple enough. If it's a calculation you often have to do, get a calculator like an accountant, or a scale or table.

For more info on definitions, see:


"In 1958, a conference of English-speaking nations agreed to unify their standards of length and mass, and define them in terms of metric measures. The American yard was shortened and the imperial yard was lengthened as a result. The new conversion factors were announced in 1959 in Federal Register Notice 59-5442 (June 30, 1959), which states the definition of a standard inch: The value for the inch, derived from the value of the Yard effective July 1, 1959, is exactly equivalent to 25.4 mm."

So nowadays, it's the inch that's defined in terms of a fraction of a meter. The meter is defined in terms of the speed of light, and the wavelength of a photon emitted by a cesium atom going from 1 ground state to another (it has 2 ground states). Those are things that could be measured anywhere, not just on Earth.
 

boatgeek

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What I'd like to see is a ruler with very thin markings. Someone should research (or look up) just how thin a marking can be while staying visible. And figure out what colors are best for this purpose. Maybe flurescent, or even back-lighted.
One part of my job is using a ruler to measure to 0.01"* in the field. I find it a little easier to use a ruler graduated every 0.02" since it's easier to distinguish the markings and take odd hundredths when the drawn line lands between the marks. We do have a scale that's graduated in 0.01" with large marks every 0.05"; medium marks at 0.02", 0.03", 0.07", and 0.08"; and small marks in between. That's OK, and far easier to read than marks at straight 0.01" increments.

* In reality, our precision is probably in the range of 0.02"-0.03", but recording to 0.01" makes our lives somewhat easier.
 

Blast it Tom!

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Hi @Blast it Tom!,

Actually, I didn't know that about James Watt. Could you kindly provide some background or more information. Do you know what year he said this? Do you have a quote from him on this topic? I am really curious.

Thank you.

Stanley
Stanley, I 've been trying to find it, but even though it was a link on here, I can't even find it on "the Google". Then I remembered it may have been Whitworth, which makes more sense time wise, but I still can't find it... so I may be full of hot air. Overall not a bad idea, but still, once you got to volumes and such ( a cubic inch would be 15.625 cc), it'd start getting ugly again....
 

MetricRocketeer

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Stanley, I 've been trying to find it, but even though it was a link on here, I can't even find it on "the Google". Then I remembered it may have been Whitworth, which makes more sense time wise, but I still can't find it... so I may be full of hot air. Overall not a bad idea, but still, once you got to volumes and such ( a cubic inch would be 15.625 cc), it'd start getting ugly again....
OK, @Blast it Tom!, thank you for checking.
 

lakeroadster

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What I'd like to see is a ruler with very thin markings. Someone should research (or look up) just how thin a marking can be while staying visible. And figure out what colors are best for this purpose. Maybe flurescent, or even back-lighted.

While I'd like everything to be metric, the physicist's point of view is that when a conversion is linear, be grateful, it's simple enough. If it's a calculation you often have to do, get a calculator like an accountant, or a scale or table.

For more info on definitions, see:


"In 1958, a conference of English-speaking nations agreed to unify their standards of length and mass, and define them in terms of metric measures. The American yard was shortened and the imperial yard was lengthened as a result. The new conversion factors were announced in 1959 in Federal Register Notice 59-5442 (June 30, 1959), which states the definition of a standard inch: The value for the inch, derived from the value of the Yard effective July 1, 1959, is exactly equivalent to 25.4 mm."

So nowadays, it's the inch that's defined in terms of a fraction of a meter. The meter is defined in terms of the speed of light, and the wavelength of a photon emitted by a cesium atom going from 1 ground state to another (it has 2 ground states). Those are things that could be measured anywhere, not just on Earth.

I've gotten to the point where I use my dial calipers more than I do the Engineer's scale.
 
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