All posts filed under “Mistake-proofing

Best bitter

Bitrex logo on slug pellets

Bitrex logo on slug pellets Bitrex, the world’s most bitter substance, is what’s known as a taste aversive – added to products which might seem tasty to humans (especially children) to persuade them not to drink them, or to spit out what they’ve already drunk. It’s a similar idea to the use of bitter coatings to break a fingernail-biting habit, although this would seem to involve some degree of operant conditioning/reinforcement compared to the (hopefully) one-off effect of Bitrex.

In design terms, we might class these kinds of aversives as blanket physiological design mechanisms – blanket because they affect all users (or at least do not deliberately discriminate against one particular class of user in the same way that the Mosquito does), and physiological because they are designed to leverage characteristics of the body’s responses to stimuli. A fire alarm intentionally loud enough to drive people out of an area would also fall under this category of blanket physiological mechanisms.

Neither are all such mechanisms aversive: the coercive atmospherics of using a “synthetic human pheromone designed to stimulate sales” in casinos (though the “extra oxygen” tactic is supposedly false) or even the smell of fresh bread in supermarkets are designed to encourage continued interaction.

Bitrex tasting

There’s a short but sweet bitter video of people tasting Bitrex here. Slug pellets are delicious, by the way, as long as you hold your nose*.


Home-made instant poka-yokes

Everyday poka-yoke

Update: Also known as Useful Landmines in the 43 Folders world – thanks Pantufla!

Mistake-proofing – poka-yoke – can be as simple as encouraging/forcing yourself to do things in a sequence, to avoid forgetting or avoiding intermediate steps. If you’re the sort of person who hangs a jacket or bag on the door handle, so it can’t be forgotten on the way out, puts things in front of the door so you can’t forget them when you’re going out, or at the top or bottom of the stairs so you’ll remember to carry them to their intended destination next time you’re using the stairs, you’re engaged in mistake-proofing. You’re introducing a behaviour-shaping constraint to assist your own effectiveness.

In the above photo, putting the mobile phone (on-charge) inside a shoe makes it more likely that it will be remembered when going out: the act of putting the shoes on requires the user to pick up the phone, which could otherwise be easily forgotten. Similarly, Mark Hurst (of Good Experience and ‘Broken’ fame) regularly features two very simple poka-yoke procedures in his Uncle Mark’s Gift Guide & Almanac:

How to remember if the batteries aren’t in your camera

Summary: If the batteries are dead, or aren’t in the camera, keep the battery compartment open.

Description: When you’re charging your camera batteries (in a wall charger, say), keep the camera’s battery compartment open. That way, if you pick up your camera to put it in your pocket or purse, you’ll see that the battery compartment is open and will remember that the batteries aren’t in it.

Leaving the camera battery door open

There’s also this:

How to make sure they see the papers you dropped off

Summary: Put the papers on their chair.

Description: Here’s a tip I learned years ago and have used ever since. If you want to make sure that someone sees the papers you dropped off at their desk, put the papers on their chair. The natural inclination is to drop the files on the keyboard, or beside the mousepad. What’s the first thing the person does when they get back to their desk? They shove the papers aside, onto a nearby pile. They want to check their e-mail immediately, and those papers are in the way!

But put the papers on their chair, and watch what happens: the person refuses to sit on them! They take a second to pick them up, and while they’re in-hand, the person takes a look at the files while they get comfortable in the chair. Bingo: you guarantee attention to your drop-off.

Papers on chair

Of course the papers-on-chair method can also be used to remind (or discipline) yourself about dealing with important papers.

This kind of very simple sequencing poka-yoke comes almost naturally in our everyday lives, at least with certain tasks. Sometimes it’s simply reminding ourselves to do something (e.g. putting a Post-It note somewhere we can see it); other times it’s trying to prevent us proceeding until some action has been taken (e.g. putting a Post-It note right in the middle of the computer screen so we can’t ignore it). Donald Norman’s Things That Make Us Smart has some interesting discussion of the power of Post-It notes and their importance as “information in the world”, disburdening some of our mental load – also part of the whole Getting Things Done phenomenon.

Sometimes we even (consciously or otherwise) try to ‘trick’ ourselves into behaving how we want to (or know we should) – the random offset alarm clock (patent; Halfbakery discussion) and Gauri Nanda’s “runaway success” Clocky being examples that spring to mind. (I once had a bedside clock radio where the button to set the minutes no longer worked, which meant that I could only set it either on-the-hour, or, because I forgot to do it at the right moment, set it maybe between 5 and 30 minutes fast. That meant that there was an uncertainty built into every time I glanced at the display, and indeed every time the alarm went off. I was rarely late, as a result.)

I have a hunch that almost trivially simple sequencing poka-yokes (in particular) could be important in designing for sustainable behaviour, such as reducing energy use and waste generation. For example, if your rubbish bin had a recycling box built into the top, so that you had to lift it out of the way (hinged, perhaps, to make it hassle to remove entirely) before putting anything into the main bin, it would be difficult to ignore the recycling box. Hence, learning as much as possible about different methods people use to mistake-proof themselves, or shape their own everyday behaviour, is likely to be useful in exapnding this line of research.

So, what are the everyday home-spun (or otherwise) tricks you use to help mistake-proof yourself?

Spear’s Spellmaster: Poka-yoke in the classroom

Back in September we looked at Mentor Teaching Machines, a clever type of non-linear textbook from the early 1970s which guides/constrains the user’s progression, in the process diagnosing some common types of misunderstanding and ‘remedying’ them. The comments were enlightening, too: there’s a lot more history to programmed teaching texts and programmed instruction than I realised, and I will certainly be covering some of this, and what useful design principles and inspiration can be drawn from it, at some point.

Now, this is not in the same league, but interesting nonetheless: a ‘game’ to teach children (4 years onwards) spelling using a poka-yoke technique. The Spellmaster, from J W Spear & Sons – the example here is from 1980 (the Enfield factory was closed after a Mattel takeover in 1994) featured eighty plastic letter tiles, Scrabble-like but larger, with raised pegs underneath, a different pattern for each letter.

Spear's Spellmaster

Spear's Spellmaster

Spear's Spellmaster

Spear's SpellmasterSpear's Spellmaster

The letter tiles are used to spell the names of objects and concepts (colours, numbers) illustrated on punched cards which fit onto a backing board, the tiles only fitting in their spaces correctly if the pegs pattern aligns perfectly with the punched holes. If the wrong letter is used, the tile doesn’t fit properly and sits at an angle rather than snapping neatly into place. The ‘snap’ of a correctly positioned letter is actually pretty satisfying – surprisingly so, given the combination of plastic (urea formaldehyde, I think) and 30-year old cardboard.

Spear's Spellmaster

Spear's Spellmaster

Spear's SpellmasterSpear's Spellmaster
Left: The wrong tile – the pegs do not align with the punched holes. Right: The correct tile – everything lines up. Below: The wrong tile here – note the extra peg on the left-hand edge of the tile, which doesn’t match up with the punched hole, and leads to the tile not sitting down properly.
Spear's Spellmaster

Spear's Spellmaster

Letters which could work either way up, such as ‘o’ and ‘s’ have – as would be hoped – symmetrical peg patterns. It’s a simple system, but it’s clever and while not offering any ‘remedial’ function to the child, I would think it’s not too likely that many children would try all 25 other letters assuming the first one didn’t fit. Hence, there is some bias against pure trial-and-error. It’s interesting to think how immediately we might consider a computer-based solution to this kind of design brief today, where a purely physical one would work very well and give a different kind of tactile satisfaction.

Spear's Spellmaster

Spear's Spellmaster

Do you really need to print that?

Do you really need to print that?
Do you really need to print that?

This is not difficult to do, once you know how. Of course, it’s not terribly useful, since a) most people don’t read the display on a printer unless an error occurs, or b) you’re only likely to see it once you’ve already sent something to print.

Is this kind of very, very weak persuasion – actually worthwhile? From a user’s point of view, it’s less intrusive than, say, a dialogue box that asks “Are you sure you want to print that? Think of the environment” every time you try to print something (which would become deeply irritating for many users), but when applied thoughtfully, as (in a different area of paper consumption) in Pete Kazanjy’s These Come From Trees initiative, or even in various e-mail footers* (below), there may actually be some worthwhile influence on user behaviour. It’s not ‘micropersuasion’ in Steve Rubel’s sense, exactly, but there is some commonality.

Please consider the environment

I’m thinking that addressing the choices users make when they decide to print (or not print) a document or email could be an interesting specific example to investigate as part of my research, once I get to the stage of user trials. How effective are the different strategies in actually reducing paper/energy/toner/fuser/ink consumption and waste generation? Would better use of ‘Printer-friendly’ style sheets for webpages save a lot of unnecessary reprints due to cut-off words and broken layouts? Should, say, two pages per sheet become the default when a dicument goes above a certain number of pages? Should users be warned if widows (not so much orphans) are going to increase the number of sheets needed, or should the leading be automatically adjusted (by default) to prevent this? What happens if we make it easier to avoid printing banner ads and other junk? What happens if we make the paper tray smaller so the user is reminded of just how much paper he/she is getting through? What happens if we include a display showing the cost (financially) of the toner/ink, paper and electricity so far each day, or for each user? What happens if we ration paper for each user and allow him or her to ‘trade’ with other users? What happens if we give users a ‘reward’ for reaching targets of reducing printer usage, month-on-month? And so on. (The HP MOPy Fish – cited in B J Fogg’s Persuasive Technology – is an example of the opposite intention: a system designed to encourage users to print more, by rewarding them.)

Printing is an interesting area, since it allows the possibility of testing out both software and hardware tactics for causing behaviour change, which I’m keen to do.

Mentor Teaching Machines: The ‘Choose Your Own Adventure’ Textbooks

Mentor Textbook Teaching Machines: Applications of SI Metric, 1971Mentor Textbook Teaching Machines: Applications of SI Metric, 1971
An Introduction to SI Metric and Applications of SI Metric, published by Mentor Textbook Teaching Machines of London, 1971.

Back in January, in a post looking at the use of forcing functions in education, I mentioned a type of textbook I remembered having somewhere which guided the user through learning in a kind of ‘choose your own adventure‘ style – depending on the answers the reader gave, he or she is routed through the book in a different order, with areas of weakness addressed in more detail to ensure better understanding before allowing the reader to progress to the next level.

At the time of the original post I mocked up how I remembered the pages looked – luckily, after a house move, I’m pleased to say I’ve now found the two textbooks I had, from 1971, and – after the jump – I’ve posted a set of photos to illustrate the system better. I love the way they’re described as textbook teaching machines (following B F Skinner’s lead [PDF]): this really is the application of machine design, or at least pseudo-programming, to a textbook, and, while I don’t know how effective the system really was in terms of advancing readers’ understanding, this type of thinking must have the potential to be relevant in other areas of interaction design…

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On the level

Patent image of Tilt sensor
A tilt-detector from this 1984 US patent, with intended application on a packing box.

The liquid detection stickers in mobile phones, which allow manufacturers and retailers to ascertain if a phone has got wet, and thus reject warranty claims (whether judiciously/appropriately or not), seem to be concerning a lot of people worldwide. Around a quarter of this site’s visitors are searching for information on this subject, and the comments on last October’s post on the subject contain a wealth of useful experience and advice.

This current thread on goes into more depth on the issue, and how the burden of proof works in this case (at least in the UK). While informed opinion seems to be that the stickers will only change colour when actual liquid is present within the phone, rather than mere moisture or damp, this may well include condensation forming within the casing, as well as the more obvious dropping-of-phone-into-puddle and so on. The main point of contention seems to be that the sticker may change colour (perhaps gradually) and the phone continue working perfectly, but when an unrelated problem occurs and the phone is taken in for repairs under warranty, the presence of the ‘voided’ sticker may be used as a universal warranty get-out even if the actual problem is something different.

Tilt detection
Along these lines, one of the posts tells of a similarly interesting design tactic – tilt-detectors on larger hardware:

30 years in the IT industry and associated customer service tells me they are trying it on and most people buy it. In the olden days, hardware used to come with a similar red dot system indicating the kit had been tilted more than 45 degrees and the manufacturers claimed the kit could not be installed and had to be written off.

Of course, 99.9% of the time the kit was fine, but they had a get-out from a warranty claim or so they thought. When the buyers tried to claim on their insurance or against the transport companies insurers the loss adjusters got involved and invariably the kit was installed and worked fine for years rather than the insurers paying out.

In some cases, of course, tilt-detectors were (are still?) necessary in this role. A piece of equipment with multiple vertically cantilevered PCBs laden with heavy components – relays, for example – might well be damaged if the PCBs were tilted away from the vertical. Certainly some devices with small moving coil components would seem as though they may be damaged by being turned upside down, for example. (Do the ultra-fine damper wires on an aperture-grille CRT monitor such as a Trinitron need to be kept in a particular orientation when handling the monitor?)

This patent, published in 1984, from which the above images were extracted, describes an especially clever ‘interlock’ system using two liquid-based detectors arranged so that if the device/package is tilted and then tilted back again, the second detector will then be triggered:

…it is desirable that the tilt detectors not be resettable. In particular, it must be possible to combine a package with at least a pair of the tilt detectors such that attempting to reset one would cause the other to be tilted beyond its pre-determined maximum angle so that the total combination would always afford an indication that the tilt beyond that allowed had been effected.

This is something of a poka-yoke – but as with the phone liquid-detection stickers, it’s being used to detect undesirable customer/handler behaviour rather than actually to prevent it happening. Other than making a package too heavy to tilt, I am not sure exactly how we might design something which actually prevents the tilting problem, aside from rectifying the design problem which makes tilting a problem in the first place (even filling the airspace in the case with non-conductive, low-density foam might help here).

But there’s certainly a way the tilt-detector could be improved to help and inform the handler rather than simply ‘condemn’ the device. For example, it could let out an audible alarm if the package or device is tilted, say, 20 degrees, to allow the handler to rectify his or her mistake before reaching the damaging 45 degrees, whilst still permanently changing colour if 45 degrees is reached. In the long run, it would probably help educated users about how to handle the device rather than just ‘punishing’ them for an infraction. I’m sure that mercury-switch (or whatever the current non-toxic equivalent is) alarms have been used in this way (e.g. on a vending machine), but how often are they used to help the user rather than alert security?

The patent description goes on to mention using tamper-evident methods of attaching the detectors to the device or packaging – this is another interesting area, which I am sure we will cover at some point on the blog.