Don't use 7-segment displays (PDF)

[ledtester]

https://harold.thimbleby.net/cv/files/seven-segment.pdf

Seven segment number displays are ubiquitous and popular. They make economic sense: they are simple, and with only seven on/off segments, they require little wiring and electronics to support. They are cheap to buy and cheap to use; they make seemingly effective products. We show how seven segment may be more or less dependable, and suggest some improvements to standard designs. However, we argue that for dependable domains (healthcare, avionics, etc) and for handheld devices that may be used in dependable domains, seven segment displays should not be used. The paper includes many recommendations for developers and purchasers.

[mendip_discovery]

Lol, once you lot can learn to write the date correctly then you can comment on how stuff is displayed.

I don't see segment displays being any worse than others. I have had many issues with various displays in the past and it comes mostly down to the use of good fonts and other things to help you work out which way up it should be.

EDIT: Damit, just looked at who wrote it. Bleeding Welsh. I wouldn't trust them either, they add far too many consonants to words for my liking.

[coppercone2]

I mean, you could also inscribe the chassis to show you logically which way is up with a logo or something. 

[Kim Christensen]

Some pretty lame arguments in that article.
I mean, who the heck would use a backwards C to represent 2, or a Y as a 4, for the 7-segment "font"? (page 2)  

Figure 2: A pen with a clock showing 12:01 or 10:21?

I guess an absolute moron, or someone with terrible eyesight, would have difficulty seeing that it's upside down. 
Same goes for their handheld blood glucometer example: 901 vs 106 could also be confused on an upside down graphic display.

There are plenty of good reasons for not using a 7-segment displays. They should have stuck to those and left these marginal arguments out of it.

[thm_w]

I don't get the "never display 0." thing, wouldn't the decimal point help clarify which direction is up?

[coppercone2]

Some pretty lame arguments in that article.
I mean, who the heck would use a backwards C to represent 2, or a Y as a 4, for the 7-segment "font"? (page 2)  

Figure 2: A pen with a clock showing 12:01 or 10:21?

I guess an absolute moron, or someone with terrible eyesight, would have difficulty seeing that it's upside down. 
Same goes for their handheld blood glucometer example: 901 vs 106 could also be confused on an upside down graphic display.

There are plenty of good reasons for not using a 7-segment displays. They should have stuck to those and left these marginal arguments out of it.

they do have a slight point because for some home medical devices someone might be suffering from some kinda blood sugar issue. But seriously it just takes 2 minutes to make a design obvious. Don't make things symmetrical? Usually they do a stopwatch type shape that holds in a particular direction. The hand closes into a cone, it is not a parallel jaw vise. The pinky is shorter then the pointer finger. Humans are actually not comfortable holding squares and rectangles, it ideally should be tapered, in addition to the rounding. Your pinky is never in a natural position holding for instance a i-phone! It should be shaped like a tie!

[SiliconWizard]

Well, they make a few valid points, which are pretty basic usability stuff and would have taken half a page to list.

But sad state of academia these days, where you have to publish stuff even when you have nothing to say.

[krish2487]

I was tired and sleepy and could not be bothered to respond to this thread yesterday night and it looks like almost all the responses are  in tune with my thoughts.. :-D

@siliconwizard

True, but thats more on the usability and design aspect of the device as a whole rather than the sole flaw of a 7 segment display isnt it ?


As a counterpoint in general, I would wager that for enunciators for industrial controls and such critical infrastructure, gimme a well designed 7 segment displays over a high resolution clunky, cluttered lcd display anyday. Hell, for that matter I prefer that even in automobile dashboards over a fangled ipad as a console. same goes for physical buttons vs touchscreens. I digress but I hope this makes the point,
 like coppercone2 mentioned, UI / UX for the physical device has more to do with the usability aspect of the widget than just the seven segment displays.

[Phil1977]

Sorry to say it provocative, but I can't help this time.

If a health-worker is too stupid or exhausted to read a display, then it´s not the fault of the display.

Please send children to good schools and qualify people who do life/death decisions. Qualify them to understand what's happening and not to be just a soft-skinned robot who gives a drug after reading *one" value.

Don't get me wrong, usability and fail-safe-architectures are important. But humanity got where it is today with caution, self-responsibility and qualifying experts you usually can trust. I´m totally serious, I'm afraid if we really think we can make everything absolutely foolproof, we just get greater fools.

[coppercone2]

oh yeah its not good to enable zombies because their gonna make some other mistake then reading the equipment wrong at that point

that's like putting the medical process on a hair trigger

works for a bit maybe but then you know after fatigue really sets in they are under budgeted because they managed to bullshit their way through the qualifications about how many hours of quality labor they can actually provide.

[Haenk]

"Acknowledgements Funded by EPSRC Grants EP/F020031/1 and EP/G059063/1"

Damn, I have the wrong job.

Sure, using only 7 segments does have weaknesses, but they have so many benefits (being cheap, easy to manufacture and implement) I don't see a reason not to use them.
Just imagine your 8.5digit multimeter using - what - analog scales for displaying the measured value?

[mikeselectricstuff]

What a waste of time. Are there any reports of actual harm caused by mis-reading a seven-segment display?
I would suggest more harm would be caused by mandating other, more expensive solutions, reducing availability of equipment available for a given budget.

Figure 1: Infusion pump, an Upreal UPR-900....
. (v) A bespoke display panel was used; it
would have been safer, easier to read, more versatile, and
cheaper had a hi-res display been used (see section 4).

Clearly no clue about how products are actually built

[Psi]

I prefer the 5x7 matrix LED digits, and a MCU to drive them.
Much more flexible. Though obviously not as cheap.

I guess the kids today would want RGB addressable matrix digits 

[TomKatt]

I prefer the 5x7 matrix LED digits, and a MCU to drive them.
Much more flexible. Though obviously not as cheap.

I guess the kids today would want RGB addressable matrix digits 

I'm glad I got a Micro Dot Phat before they sold out and the displays got stupid expensive...

And I wish more products reverted back to old school red 7 segment displays. 

[pardo-bsso]

Just imagine your 8.5digit multimeter using - what - analog scales for displaying the measured value?

I think that four analog meters ought to suffice for that. (looking at my bag of scrap for inspiration...)

[Siwastaja]

Are there any reports of actual harm caused by mis-reading a seven-segment display?

I don't know about exact evidence, but see e.g. Varig Flight 254 for demonstration how important the proper representation of decimal points can be, and what kind of mistakes trained personnel can make. It is certainly true that decimal points as used in seven segment displays are small, and if multiplexed to same brightness as other segments, easily remain unseen. Combine this with confusing spacing with number 1 (which has two options, both of which space weirdly).

Unlike others who get defensive for some reason I can't understand, I think this article is spot on and provides pretty good points. For example, I would not use seven-segment displays to represent large floating point numbers where the decimal place varies. I would also avoid any use where other text (On, oFF, Error) is needed, it always smells like hacking a cheap substitute for a real display. In such case, if modern high-res digital raster display is out of question, do what safety critical applications (e.g. nuclear control rooms, cockpits) have always done: dedicated text displays with etched mask, backlight with at least two independent bulbs; analog needle meters for those functions where analog is suitable; and seven segments for the rest.

For applications which show 3-4, maybe 5 numbers tops, with decimal place fixed in one place, seven segment displays work fine if you take care of the basic precautions as listed in the paper (good contrast between unlit/lit segments, no visual blocking of edge segments when viewing at an angle...) ... but seeing the defensive knee-jerk reactions of the forum, I'm pretty sure most here have never considered such things at all, and designed many nearly illegible displays as a result.

[coromonadalix]

same here for the doc link,  some good facts and some sh$%#$%

more alarmist than nothing ... 

you should have enough brain to understand what it means to use 7 segments display, and you simply don't write words in them
unless you have the alpha numeric ones ... and still they are not perfect
 

the good the bad the ugly   

[Phil1977]

Just to say it clearly because I think it´s interesting: The Varig-Flight seems to have suffered of a decimal point error in the flight plan, not on a 7-segment display.

And at least I don't want to defend anything old fashioned - but a general bashing of a very usable and well known technology like in the paper does not help anybody. May usability labs decide what´s really better, but I personally never had issues even with small decimal points on 7-segment-displays. But I´ve seen many really bad number renderings on TFT-screens.

If display design is to be discussed I´d like to mention something else: Dedicated 7-segment displays are often hardwired to one system parameter. If I want to know the temperature in a process oven, I can look to a dedicated position and always quickly get the value.

TFT-screens are often menu-operated and tempt the developers to use overlays or variable screen content. The time it needs to find the information on such a TFT-screen can be much longer, and that can be real problem for safety critical things. But of course that´s not the fault of the TFT-screen, as it is not generally the fault of 7-segment displays if there are reading errors.

[coppice]

Any form of information display requires care to make it clear and unambiguous. When people have a more flexible display than a simple 7 segment one, they often use that sophistication to make something fancy looking, rather than clear. 7 segment displays can work very well for normal readings. Their key downside is their very limited ability to clearly display problem reports, whether that is something like an over-range condition, or an error condition.

[PlainName]

On thing not addressed is that numbers tend to be easier to read on 7-segment displays, not because of the technology per se, or font (which actually tends to be worse than a hi-res LCD) but because they are fixed width. When a number is going up and down and the font is not fixed width OR the text is justified, the number keeps shifting left and right as it changes, so it's hard to follow and you can't take changes in at a glance - you have to actually pause to read it each time. For all it's faults, the 7-segment display doesn't suffer from that.

A great (in a manner of speaking!) example of this is the otherwise brilliant EEZ BB3 power supply, which used a proportional font AND justification for the numbers (but this has been fixed now). Very difficult to follow when it goes from, say, 10.0 to 9.75 and similar.

[Phil1977]

On thing not addressed is that numbers tend to be easier to read on 7-segment displays, not because of the technology per se, or font (which actually tends to be worse than a hi-res LCD) but because they are fixed width. When a number is going up and down and the font is not fixed width OR the text is justified, the number keeps shifting left and right as it changes, so it's hard to follow and you can't take changes in at a glance - you have to actually pause to read it each time. For all it's faults, the 7-segment display doesn't suffer from that.

A great (in a manner of speaking!) example of this is the otherwise brilliant EEZ BB3 power supply, which used a proportional font AND justification for the numbers (but this has been fixed now). Very difficult to follow when it goes from, say, 10.0 to 9.75 and similar.

That´s a real pain of many TFT-displays. With a fixed width, you can display many digits with a high refresh rate. For technology-friendly people (aka Nerds) this is nearly as intuitive as an analogue scale.

Indeed I think that many people who grew up with 7-segment displays just like them because their brain is very used to them. Of course that´s no objective advantage, but I honestly think a clear and fixed-width digital display is the best compromise of precision and readability.

[Tation]

I do value this paper, even when some of his caveats seem a bit "on the edge" for me.

But I do miss a paper describing how to sensibly display information on a LCD/TFT/whatever high resolution screen. Am I the only one infuriating every time that some engineer decided to display a fixed width number (or an hexa number) in a variable width font? Even more when many of such -related- quantities are shown stacked one in top of another (& left aligned  )

[jzx]

For me, the worst case is programmers that use 7 segment fonts on graphical displays, even in pc  programs.
Some case of the pdf are a bit extreme, for example, the infusion pump has no contrast filter? I think that is no so cheap device to no afford for a bit of plastic.

[mikeselectricstuff]

For me, the worst case is programmers that use 7 segment fonts on graphical displays, even in pc  programs.
Some case of the pdf are a bit extreme, for example, the infusion pump has no contrast filter? I think that is no so cheap device to no afford for a bit of plastic.

and on oscilloscope screens, just because it's a DVM mode

[Siwastaja]

Just to say it clearly because I think it´s interesting: The Varig-Flight seems to have suffered of a decimal point error in the flight plan, not on a 7-segment display.

Obviously yes, but the fact that decimal points are already dangerous, the typical 7-segment display making them very small replicates that danger. There are solutions to this, for example making the decimal point bigger, brighter, adding dead space in the correct place (i.e., where the point is), or showing the digits after the decimal point in smaller fonts (i.e., using smaller 7-segment displays for decimal part, but then you need fixed decimal point location, which isn't a bad idea), and the article discusses most of these points, if you read it.

One thing which is unavoidable and unsolvable in 7-segment displays is addition of "random" spaces around number 1 (you can choose which side it is added to, but if you do it dynamically, users are even more confused). That acts as a mental separator (thousands or decimal), want it or not. Now if this is your only problem, then fine, but add this to poor design choices like a very small decimal dot, driven too dimly, and switching the place of the dot dynamically to any unexpected place, and the likelihood to read it wrong is even larger than on a paper - and even on paper, decimal points are sometimes read wrong.

I suggest everyone who engineers physical user interfaces reads the paper, even if they end up preferring 7-segment displays. People who get offended by the clickbaity title should just ignore the title. (I would have preferred "7-segment displays considered harmful".)