Coins vs Rulers for scaling (Migrated)

UPDATE: This got migrated into it’s own thread so the context is I’m poking fun at @Pharap because he has mentioned a couple times he doesn’t like the use of quarters for scale.

I believe the pictures intent is to show a general scale so that it is instantly understood that it is not the size of a house. Most people are going to have a more immediate and visceral reaction to seeing something next to a coin, because they interact with and have a good understanding that a coin is something that is small at an emotional level more than a practical one.

That emotional connection, I think, gives the product a sense of familiarity or cuteness to it. But as you have identified those are probably strongly tied to culture and when you don’t have that benefit it is jarring enough to wonder why a more appropriate object isn’t used.

I mean, the whole “banana for scale” thing is pretty much proof that this kind of thing is prolific on the internet and we all understand how silly it is.

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Perhaps, but coins can be drastically different in size:

If you don’t know the currency then the you don’t have a good idea of how big the coin is in the first place.

(I’ve purposely used some old coins here to illustrate the point that someone who isn’t familiar with the currency would have a harder time identifying which coins are the more modern coins.)

That’s precisely my point.
Coins are only useful to people who are used to handling them.
If somone has never encountered a euro or a quarter then you might as well be using drachma for scale:

If people understand that it’s ridiculous then they shouldn’t proliferate it.

For the sake of spending a few minutes to find a ruler they could make everyone’s life easier:


I’m doubtful that it would get much reaction, coins are a kind of mundane thing that most people see every time they go shopping.
Maybe I’m just particularly apathetic towards that sort of thing though.

I mean you’re not wrong, sure but again, it’s a relative scale. It shows you at a quick glance that the thing is very small. If you figure that a majority of the sales for any retailer is going to be their domestic market it actually makes more sense from a visual perspective. It would actually take me more time to get a rough estimate of the size of a thing if there were a ruler, as I’d have to actually read the ruler or at least identify the tick marks on it.

And actually, I have exactly 0 rulers in both my house and my office, but a hell of a lot of quarters.

From a purely photographic / aesthetic standpoint using a coin allows you to frame the whole shot without having to crop the ruler, which for a lot of people is a massive benefit.

I could imagine people being just as particular about having clean white space around their photo as they are about using a universal measurement.

Furthermore, it’s probably worth mentioning that all forms of measurement are relative. Your ruler is going to be minutely different than mine and even scientists argue about the exact exact standard weights down to insanely small decimal points.

What I’m saying here is nothing matters, embrace the chaos, darkness is the only absolute.

EDIT: What if I used a ruler with INCHES? Wouldn’t that almost be worse?

Nope an inch is an inch and I’m old enough to use them. At least an inch is an inch anywhere outside the clothing industry who seem to have varying inches even within the same items.


If you’re designing an object (e.g. a 3D printed shell) then you need to know precisely how big a board is to know if it will fit.
“Very small” isn’t precise enough for design work.

Imagine if you tried to build the Arduboy’s shell without knowing precisely how big the guts were going to be,
just roughly how big they are compared to the coin of a foreign currency.

Identifying the numbers on a ruler would take no more time than identifying a coin.
You don’t have to count the notches, every ruler has numbers printed on them.

In the era of online shopping where companies will ship to other countries they ought to be making an effort to consider the needs of those other countries.
If they only target their domestic market then they’re not making the most out of having an online shop.

I have at least three rulers on my desk, plus a set square, plus another ruler and two more set squares in a drawer.
There’s also probably some tape measures in a drawer somewhere.

Go out and buy a ruler, you could spend one of those quarters and still get change. :P
At the very least you would be able to draw straight lines.

How exactly is that a benefit?
It doesn’t matter if you crop off the far end of the ruler because the larger values are irrelevant.

That’s not exactly hard either, just chuck a piece of A4 on a table.
Having decent lighting is the real challenge.

They are, but not all are standardised or in global or even common use.
Having units that are globally recognised and generally in common use is important.

Not enough to be perceivable by the human eye.

As @Keyboard_Camper said, inches are also standardised and well-recognised,
so no, it’s not worse than using coins.

It’s not as good as centimetres because less countries use inches,
and SI units are the standard for doing anything science-related,
but at least there’s a fixed inch to cm ratio if someone wanted to convert the units.

Also the majority of rulers have both centimetres and inches anyway.

Another reason for not using coins - coins are generally circular, which makes it harder to judge the scale by sight because you end up comparing height/width to diameter.
Using something with a flat edge makes it easier to see the scale because you’re comparing height/width to height/width.

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No self respecting engineer or cad designed is going to do anything short of rudimentary mockups from pics online whether with coins or even a ruler in the shot (though I agree the ruler would give you a much better shot). Too much variability in a camera shot in terms of angle tilt and skew that would add too much error to give any meaningful dimensions unless you program an entire algorithm to detect, correct for errors and estimate dimensions but by that point a mountain is made from a molehill. Either need calipers and a sample board or dimensional drawings to get anything reasonable designed.

Also wondering why we are even still arguing about coin vs ruler. Obviously one is more for artistic effect and the other to convey more accurate sense of size. They are both things that exist.

No, but having a ruler next to the board (with markings indicating globally standardised units) is going to make designing those rudimentary mockups easier than having to use pictures of the board next to a coin of a foreign/unfamiliar currency.

The error would be on the order of millimetres.

It’s enough error that it’s not what you’d use for the final design,
but it’s not enough error to make decisions about whether the board is a suitable size for the intended application.

To get something within millimetre precision when you actually have the board to work with yes,
but you have to actually buy the board before you can measure it manually.

Originally I was just making a joke.

Artistic merit is entirely subjective.

That’s half my point, pictures of boards against rulers are actually scarce compared to the number of pictures of boards against coins.

Often sites will also supply dimensions, but not always.

The company I work at does a lot of mechanical and electrical engineering, including cad modelling for adapting medical instruments to our product and you’d be surprised the hoops we have to jump through to get any technical info about newly released scopes to confirm compatibility with our system or create interface adapters. It ends up being easier to just rent said equipment from the manufacturers so we can do the measurements ourselves. No way we could purchase each and every scope as they retail for hundreds of thousands of dollars each and there are a handful of new or updated models released periodically which would make the prospect financially impossible to go that route.

I’m not really surprised, I know people in general are pretty terrible at documenting things.
The amount of commentless code out there is a testament to that.
(And various hardware datasheets. I find datasheets tend to be a bit vague/unspecific in places.)

But there’s quite a bit of difference between a company of professionals working with expensive, important machinery and your average (potentially cash-strapped) hobbyist.
Hobbyists can’t exactly rent boards from Sparkfun, Adafruit, Pimoroni et cetera.
If a hobbyist orders a board and it’s not the right size for what they want to do with it then they end up either potentially out of pocket or having wasted a lot of time.
Granted, size isn’t always important, but for some applications it’s very imortant.

(I decided this is finally big enough to warrant splitting the topic.)

This is why as a hobbyist I rarely start designing something without the necessary parts in hand so I can verify my design will all fit and work together before wasting time. What you describe I would think of as “sizing” or “characterizing” components which belong in the prototyping stage well before you get to designing anything substantial. Of course this means I have to put money down upfront and on occasion I end up with parts I can’t use that go in storage until I find a project that will work with them. Maybe I’ve been lucky though, but for the most part I am able to make compensations in the design to get things to work in the end or at the very least bodge them. I’ll admit there is certainly a level of intuition to the design process that helps in situations like these to avoid missteps in part selection.

… lol I feel like there’s some sort of inappropriate joke one could make about this statement but I’ll suppress the urge …

Even prototypes need to have at least a rough design first.
Otherwise you’re just grabbing parts and trying to mash them together.

At which point being able to have a good size estimate (on the scale of centimetres) would be useful.

I (for one) have neither the money nor the space spare to do this.
It probably makes sense if you’re building circuits regularly and have your own little workshop.

Frankly I’m surprised it didn’t crop up sooner.

Maybe the area I’m in (embedded hardware) is different, but at the prototyping stage I am just concerned with electrical specifications and getting a rough software base up and running on breadboard hardware as a proof of concept to see if the project is practical and worth doing. At the prototyping stage only a rough sizing of parts is sufficient. I don’t actually begin case design and cad modelling each component to figure out 3d placement within an enclosure until after this step is done at which point then having dimensional accuracy become necessary. Now I tend not to use modules, but raw chips and components which mostly are very well documented in terms of footprints so maybe I just tend not to have these size issues in my projects.

Yeah, as a youtuber who does projects regularly, having a well stocked lab in my spare room makes a lot of sense for me.


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Still better than a coin becuase lego figures are easier to get ahold of than coins of a foreign currency.

(But still not as good as a ruler, of course.)


Not all Lego men are the same size …


If only someone could take a picture of a minifig next to a quarter we would be able to in turn translate the terrible adafruit product pictures to the universal minifig scale.

We have a phrase for this situation…
“Oi, leave it alone you bloody little toerags!”
Or, more concisely, “Bloody oiks!”.

Seriously though, I think giant lego men might be rarer than foreign currencies.
Unless you live in Windsor of course.

Or just send Adafruit letters threatening to coat their doorhandles in marmite and steal their left socks until they rectify the problem.

Just use a piece of string everyone has access to a piece of string.

I suggest that we start using Arduboy as a standard unit of measurement.

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Presumably you have to measure it with a piece of string?
In which case you’ve got a bit of a bootstrap paradox.