User interface design for vending machines


How hard can it be to design the user interface of a vending machine?

You accept money, you have some buttons, the user pushes the button, they get their product and their change.

At least in the United States, many vending machines arrange their product in rows and columns (close-up view). To select a product, you type the letter of the row and the number of the column. Could it be any simpler?

Take a closer look at that vending machine design. Do you see the flaw?

(Ignore the fact that the picture is a mock-up and repeats row C over and over again.)

The columns are labelled 1 through 10. That means that if you want to buy product C10, you have to push the buttons "C" and "10". But in our modern keyboard-based world, there is no "10" key. Instead, people type "1" followed by "0".

What happens if you type "C"+"1"+"0"? After you type the "1", product C1 drops. Then you realize that there is no "0" key. And you bought the wrong product.

This is not a purely theoretical problem. I have seen this happen myself.

How would you fix this?

One solution is simply not to put so many items on a single row, considering that people have difficulty making decisions if given too many options. On the other hand, the vendor might not like that design, since their goal is to maximize the number of products.

Another solution is to change the labels so that there are no items where the number of button presses needed do not match the number of characters in the label. In other words, no buttons with two characters on them (like the "10" button).

Switch the rows and columns, so that the products are labelled "1A" through "1J" across the top row, and "9A" through "9J" across the bottom. This assumes you don't have more than nine rows. (This won't work for super size vending machines - look at the buttons on that thing; they go up to "U"!

You can see another solution in that most recent vending machine: Instead of calling the tenth column "10", call it "0". Notice that they also removed rows "I" and "O" to avoid possible confusion with "1" and "0".

A colleague of mine pointed out that some vending machines use numeric codes for all items rather than a letter and a digit. For example, if the cookies are product number 23, you punch "2" "3". If you want the chewing gum (product code 71), you punch "7" "1". He poses the following question:

What are some problems with having your products numbered from 1 to 99?

Answers next time.

Comments (75)
  1. Anonymous says:

    This is a very serious problem, it is the case on the vending machine downstairs from me, and its happened to me many times (although not much in the last few years).

  2. Anonymous says:

    Certain numbers are "unlucky", for example 13, and people avoid them. Some hotels don’t have a 13th floor for this reason.

  3. Anonymous says:

    The columns are labelled 1 through 10. That means that if you want to buy product C10, you have to push the buttons "C" and "10".

    Every place I’ve seen this (including your monster vending machine, the columns were labelled 1 to 0. Problem solved.

    One thing I don’t get – when vending machines dedicate whole rows to a single product, why not just give the whole thing a single code and have the machine decide which item to drop?

    > What are some problems with having your products numbered from 1 to 99?

    Nothing, really. Have the user punch in their product code and hit vend. Once they’ve put in a product code, light up a led by their chosen item. If they make a mistake, they can always hit cancel.

  4. Anonymous says:

    Problem with 1 to 99? The difference between "1" and "11," "2" and "22," et cetera. If they have to wait after pressing "1" or hit some "Enter" key, then they may hit 1 again in frustration and choose number 11. Number them from 10 – 99. Problem solved :)

  5. Anonymous says:

    Is it me, or can you not get the user to enter C01 thru’ C09, and then C10, C11 etc… Have I missed something?

  6. Anonymous says:

    This wouldn’t solve the real problem. The fact that many items get stuck on that corkscrew thingy.

    The other more serious problem, though related, is the many fatalities caused by tipping a vending machine in order to release said stuck product.

    We should solve these issues before we worry about the problem of dialing a wrong number.

  7. Anonymous says:

    Number the columns 0 to 10.

    Or, have a column on the left called begin(), and a virtual column to the right called end(), then they loop through till they find the one they want.

  8. Anonymous says:

    Just label all the items with Huffman codes. Then you get the added bonus of assigning shorter codes to frequently-purchased items. :)

  9. Anonymous says:

    I would like to see the product package/logo/name/whatever and a button just below it. Add a display for the number of items left and a big EMPTY if it is out. No need for a big glass covered peek hole into the machine.

    Most soda vending machines are like that so why not for other stuff?

    No need to worry about numbers, columns and everything else that can go wrong…

  10. Anonymous says:

    If I recall correctly, the reason they don’t use purely numbers is that some people confuse the price and the code. So if there’s an item for 50 cents and its code is 23, the person types in 50 by mistake.

  11. Anonymous says:

    Instead of numbers, use letters. Starting with AA, AB, AC, etc. and ending with whatever you need. Maximum, of course, is ZZ. This way you can have up to 25×25 = 625 combinations.

  12. Anonymous says:

    What are some problems with having your products numbered from 1 to 99?

    First of all, remove all one-digit options. So it’s now 10 to 99.

    Second, remove all XX numbers, like 22, 33, 77 to avoid the bounce-effect problem.

    This way, I see no problems. Am I wrong?

  13. Anonymous says:

    See URL for a related BOFH episode.

  14. Anonymous says:

    We had a snack machine that (IIRC) used all numbers, but none of the numbers ended in a 0 or a 5. This way the item number and the price could not be confused (which I almost thought I had done once). The numbers started at 11, so you didn’t have to worry about how to distinguish between 1 and 11–everything was two digits.

  15. Anonymous says:

    The other more serious problem, though related, is the many fatalities caused by tipping a vending machine in order to release said stuck product.

    Is this all that common? Every vending machine related fatality I’ve heard about has been from trying to get free stuff, which, when you think about it, isn’t really that big a deal.

  16. Anonymous says:

    I say forget the input alltogether. Make people exercise for what they want. Just put a treadmill in front of it. The higher fat/calorie value is on a snack, the harder they have to work for it. As they progress on the treadmill, they would be able to see which products are currently available to them and can decide to stop or work for something better.

  17. Anonymous says:

    Other minor design flaws include having the decimals in the price in red. It makes the customer "see" 99 instead of 01 when the price is 1.99. Psychologicaly you want to "hide" 99 and have the customer only perceive 1 while the price is actually ~2.

    Also, what is the little opening below button 10? And the small button further down?

    Another funny thing is that it has 6 rows of products and only 5 letters (A-E)… Okay so the last row seem to be disabled or something though, but still strange.

  18. Anonymous says:

    Steve Maguire covers this in Writing Solid Code (Microsoft Press). The relevant chapter is called "Candy Machine Interfaces".

    I’ve been thinking of entering bug reports for our new vending machines. The new Coke machine won’t return your money if the variety you want is sold out. Instead you have to purchase another item. It doesn’t show sold-out indicators until you insert your coin(s) and try. (The old Pepsi-branded machine got this right with indicators and the ability to get your money back.)

    The adjacent candy machine won’t accept bills when there’s not enough change in the hopper, which makes sense, but it will accept more coins than the price of the item, so you can spend 75 cents on a 60-cent bag of M&Ms. I’m not sure if that’s a bug or a feature. Sometimes I’m desparate enough to overpay for my chocolate fix.

  19. Anonymous says:

    I think you’re wrong. As soon as you start removing options, your options for organizing the products intuitively decrease dramatically.

  20. Anonymous says:

    A friend of mine with a small child showed me a "learn to count" book which he’d received as a present. One of the pages asked "how many blocks do you see?" and then had blocks labelled 1, 2, 3, 4, 5, 6, 7, 8, 9, 1 and 0, with the last two real close to each other. I see eleven blocks. Of course, you were intended to see ten blocks.

    You don’t need a degree in child psychology to figure out that this is a BAD idea.

  21. Anonymous says:

    Other minor design flaws include having the decimals in the price in red. It makes the customer "see" 99 instead of 01 when the price is 1.99. Psychologicaly you want to "hide" 99 and have the customer only perceive 1 while the price is actually ~2.

    You never price vending items as x.99 – it’s always something easy to pay for with large coins.

    > The new Coke machine won’t return your money if the variety you want is sold out. Instead you have to purchase another item. It doesn’t show sold-out indicators until you insert your coin(s) and try.

    If you punch a sold out item with no change loaded, does it light the sold out light?

  22. Anonymous says:

    I’d like to see a APL version

  23. Anonymous says:

    The vending machines around campus here use three digits. Also, I believe the system is also designed to interface with another vending cabinet not equipped with a keypad or money system.

    They also have a photosensor to detect when the thing jams. Actually, I’ve purposely selected items likely to jam because often when the system detects this and revends, the first item falls out along with the one behind it.

  24. Anonymous says:

    The worst user interface, in my opinion, is the Metrocard vendingmachines in Manhattan.

    To top off my Metrocard with $20 takes 11 separate steps.

    (from memory)

    1. Click Start

    2. Click Language

    3. Click Metrocard

    4. Click Add Money to MetroCard

    5. Insert MetroCard (about 2 feet from screen)

    6. Select Cash

    7. Select $20

    8. Insert Cash

    9. Retrieve Metrocard

    10. Click Done

    11. Click No receipt

    Even though this is usefull for first-timers, what Id like is this:

    1. Insert Metrocard

    (system remembers actions and language from first time)

    displays ‘Add $20 to your card (no reciept) – Just insert cash’ or ‘select other action’

    2. Insert cash

    3. Retrieve card

  25. Anonymous says:

    Use a 4 way toggle button (like on a game pad) to select the product, with bright LEDs under each choice to indicate the current selection. A big "BUY NOW" button next to it could indicate the purchase should be made. You could also include a much smaller, less noticable, ‘return my money’ button.

    As an alternative you could use 2 dials to dial through rows/columns, or a single dial to dial through all selections.

    All of these remove having to do any mapping between a code and the product. They also preserve the ability to have a single pane of glass which is likely less expensive. At this point studying which industrial design has a better feel or will induce a better usage pattern would be appropriate. I’d expect dials would probably be fun to play with and could cause more sales. However dials might have a lower MTF.

    Of course none of this addresses the serious problems of cash acceptence/return, ‘corkscrew’ or vend failure, and the very serious issue of machines falling on people as they try to beat the product out of the machine after a vend failure.

  26. Anonymous says:

    I have a better solution – assign GUID to every item. Who cares that you have to punch 32 keys to get a candy bar :)

  27. Anonymous says:

    Why not just have a button on the bottom of each column and a button to the right of each row. You push button for the column you want and then the row. The only flaw for this is if you need some rows with different width slots. In that case, you can just make the slot a multiple of the standard column width.

  28. Anonymous says:

    Dino said above to use letters up to ZZ. that has the same problem as the numbers.

    I’m in a class at the UW extension in bellevue. There’s a vending machine there that has letter buttons.

    and the letter buttons go A-Z, AA-FF, i think. Either way, people press A 2x to get the thing that says AA, and get the item in slot A instead of AA.

    If you used one number and one letter for everything, you’d still need 35 buttons (i’d leave of 0 for confusing with O (1-9,A-Z). That would give you 7 rows of 5 buttons, and 234 possible items with a lot less confusion. technically, you could use numbers for rows, letters (excel style) for columns and reduce the buttons considerably.

  29. Anonymous says:

    "The vending machines around campus here use three digits. Also, I believe the system is also designed to interface with another vending cabinet not equipped with a keypad or money system."

    That’s what’s in the building I just moved to. The tree digit keypad-style seems to work pretty well; I haven’t punched in the wrong code yet. It also has a side refridgerated cabinet with no keypad or money system. Handy for buying ice cream sandwiches. :)

    "They also have a photosensor to detect when the thing jams. Actually, I’ve purposely selected items likely to jam because often when the system detects this and revends, the first item falls out along with the one behind it."

    I wish we had that. I love Red Vines, and those packages are the worst for jamming; usually you have to buy 2 or 3 to get the first one out.

  30. Anonymous says:

    "Why not just have a button on the bottom of each column and a button to the right of each row."

    Not being a particularly tall person, I may have trouble buying anything from the top row if that were the design…

  31. Anonymous says:

    This happened to me today.

    I’m on a new years diet. So this morning I dutifully went to the vending machine to get a healthy fruit & nut bar for breakfast. I tried to press 51 but the machine decided I’d pressed 55, so I ended up with Cadbury’s milk chocolate.

    My diet is ruined & I blame computers

  32. Anonymous says:

    I noticed that our vending machine at work was quite cleverly designed (while pondering the ever difficult task of deciding what to buy ;>)

    All numbers are two digits from 1 to 9, after entering the second digit the item is dispensed.

    All prices are some multiple of 5. So to avoid the problem of a price and an item id having the same number, no item id uses 5.

    No item uses double digits, e.g. 22, to avoid the debounce issue mentioned above.

    No item uses the mirror of another item id. e.g. there’s a 12 but no 21, to avoid typos.

    The only thing they don’t seem to do which might improve matters would be to not use a number which is near another number in the 3×3 grid, e.g. if the first number is one, then don’t use 4 and 2 in case the punter accidentally pushes either one while pressing 1… Although that would reduce the schemes usefulness for larger vending machines…

  33. Anonymous says:

    "Why not just have a button on the bottom of each column and a button to the right of each row. You push button for the column you want and then the row."

    I got a better idea. have a laser pointer with a button. the user points the beam to an item, the bin acknoledges with LED flasing, then user presses a button. if his hand tweaks a little while pressing it, he gets the wrong thing ;) delay will help in this case, actually.

    Or, better yet, have the whole front panel to work as a tablet. ask users to use fingers to point and fist action to buy.

  34. Anonymous says:

    Steve Steiner suggests: <em>"Use a 4 way toggle button (like on a game pad) to select the product, with bright LEDs under each choice to indicate the current selection."</em>

    Steve, you stole my idea!

    Now to quickly run to the patent office. ;-)

    This also allows vending machine owners to sell ad space. Which item should be highlighted initially? Why, the one that pays the most! You’d want it semi-random, but certain products might be highlighted more often…

  35. Anonymous says:

    On the two digit thing: What happens when you mistype the first number? How do you undo that? The letter-number paradigm allows you to change the input value indefinitely and without a complicated interface, so long as the buttons are sensibly labeled.

    the "buttons around the window" thing doesn’t take into account differing horizontal sizes of slots – after all, gum takes up less space than a bag of chips.

    The "game pad" idea should be made so that the start point is always the same and easy to determine.

    The "tablet" idea is expensive like whoa. "fist action"? You want me to punch the vending machine? :)

    Vorn

  36. Anonymous says:

    I think the number should be coded in binary, in case the user provides an incorrect sequences he will be serviced with cyanide. =)

    (I don’t see the problem, what about a LCD display that shows your selection and asks for confirmation ?!)

  37. Anonymous says:

    Too bad accurate, speaker-independent, environmental-noise-resistant voice recognition is always 10 years away (at least it’s closer than fusion).

  38. Anonymous says:

    Did you ever read about the entire shop in England that was turned into a giant 150-item vending machine?

    http://news.bbc.co.uk/1/hi/england/tees/3184029.stm

  39. Anonymous says:

    I agree with Andreas, why do you have to show the user all the products in a big glass window? A button with a label is ok.

    Any technical problems with telling if the machine is out-of-stock on a certain item, etc, the vending machine builders must solve.

    As a software engineer we are taught not to let the implementation show through the design, why should it be any different for vending machine builders? Their machines probably meets a lot more technically inept people than much of the software that’s produced.

  40. Anonymous says:

    A button with a label is ok.

    Make that a button for each product with a label on it is better.

  41. Anonymous says:

    >One thing I don’t get – when vending machines dedicate whole rows to a single product, why not just give the whole thing a single code and have the machine decide which item to drop?

    If you do that, then the machine owner can’t change what’s in each slot later so that one row is *not* now solely dedicated to one product. And the UI for the owner to say "slot C4 and slot N7 have the same item in, so use them interchangeably" would be horrible, so you just do without it and rely on the punters to identify when a row is empty and so find another.

  42. Anonymous says:

    nonono… what we need is a robot hand that you control a la "Atari" =o)… no codes to type, you move the thing with the control and get it =o)

  43. Anonymous says:

    Buttons, schmuttons. Just use a Bic pen to open the cylinder lock and have what you want for free.

  44. Anonymous says:

    Cooney: We have Coke machines here *nearly* like that, except that the coin return button works if you’ve put money in already. Change release looks mechanical, but it’s been electronic for a while — give that button a stab next time you’re up against a sold out, and you’ll probably get your change back (although here, if you put in a dollar coin you’ll get four quarters back, seriously ruining the mechanical coin return facade!)

  45. Anonymous says:

    1/12/2005 2:56 PM Andreas Magnusson

    > I agree with Andreas, why do you have to

    > show the user all the products in a big

    > glass window? A button [for each product]

    > with a label is ok.

    Sure, it was OK for someone when I orally translated all of the button labels, but how would it be OK for that same person if no one else were there? This was on a machine inside a company, so the only users were employees of the company who obviously could read Japanese (even including me in the case of those button labels) and employees of other branches of the company who were visiting our branch.

    Machines out on the street usually show models of the products they’re vending, with a button next to each model.

  46. Anonymous says:

    As someone who has been playing video games a long time, I love the game pad idea. Even so, I don’t think vending machines should actually use it. Here’s why:

    1. It would take too long to get to products at the edges

    2. A ‘vertical’ D-pad would be really akward.

    3. It’s hard to tell what will be selected in a certain direction when products aren’t lined up in a grid–I’ve seen plenty of vending machines like this.

    4. You have the extra cost of wiring and putting in an LED for each option. Also, what happens when the vendor decides to change the layout?

    Additionally, my experience is that some people just don’t get directional pads. My father is hopeless when it comes to menus, whether they’re on games, stereos, or even DVDs.

  47. Anonymous says:

    Andreas:

    Software implementation has a one-time cost. Once you’ve written something, it doesn’t cost you (much) to make additional copies.

    Vending machines use hardware. Complex machines means a higher hardware cost. I don’t know whether the hardware costs enough that this would be an issue, though…

  48. Anonymous says:

    "On the two digit thing: What happens when you mistype the first number?"

    My three digit vending machine has a larger C/CE button, like a calculator. [picture at http://www.automaticproducts.com/GRAPHICS/LARGER_IMAGES/GLASSFRONT_SNACK/PREMIER/123_Large.jpg] From their website: "’Consumer Friendly’ Selection Assembly – Our redesigned selection panel is based on the consumer accepted telephone keypad. It makes selecting snacks and candies easier than ever."

    The company also makes the delightfully named "RoboQuencher" [http://www.roboquencher.com/]; I highly recommend watching their amusing video about it. The home page seems to suggest that glass front vending machines [being able to see the products] sell better than machines where you just have a label or picture by a button. It’s probably more conducive to impulse buying or making the products look more attractive. I think pop machines get away with not showing the products because everyone knows what "Pepsi" is. Besides, pop vending machines usually use the entire machine to display a stylized picture of the main cola it dispenses.

  49. Anonymous says:

    Jeremy: We’re talking about the same machine company. The anti-jam is their "Goldeneye" http://www.automaticproducts.com/HTML/products/golden_eye_main.html

    Interestingly, the input also times out and automatically clears after a little while.

    L.J.: Also check out "Automats", basically vending machine cafeterias in New York around the 1920s.

    Having managed to mispress soda machine buttons, I think there should be a system to make you press a button twice. I don’t think anybody would really notice that "feature" in action.

  50. Anonymous says:

    LJ: I take it you’ve never been to Japan? They’ve got lots of shops like that, and vending machines for just about anything. I hear they get rid of the used panty machines, though.

  51. Anonymous says:

    Holy cow, I highly recommend watching the roboquencher video Jeremy linked to:

    http://www.roboquencher.com/video/downloads/WMV/Robo_Quencher.wmv

  52. Anonymous says:

    romanp:

    "Or, better yet, have the whole front panel to work as a tablet."

    That was *my* line. Sheesh!

    Of course you’d want to highlight the selected item as a service to the geniuses (or is it genii? ;-) ) going "I want *this* one. Not *that* one."

    And of course you’d need a step or two at the bottom for the shorter customers :-p

  53. Anonymous says:

    Thinking outside the box here, why not have the GLASS SCREEN as a giant touch screen.

    The screen would be divided into very identifiable squares, so from front on one would literally press the box they wanted – this too will overcome internationalisation issues as well.

    But I guess there should be some feedback mechanism to identify the user has indeed selected the correct food item. And this could become rather expensive too. Just a thought really.

  54. Anonymous says:

    Just put the numbers first, followed by letters. That is, 10C, not C1…whoops.

  55. Anonymous says:

    The Japanese having those shops doesn’t surprise me, the English having one certainly does! Nation of shopkeepers?

    There’s a video of the English shop on the BBC site. I’m sure most of those shops must work the same way. Each item has a code number e.g. 1205, which gets entered on a keypad, and a robotic bucket scoots along to that item, which is then pushed off the shelf into it.

    The interface needs to be dead simple. The average ATM doesn’t have a trackball and icons. It’s easy to overcomplicate a new UI. Or to pick so many holes in an existing one that you convince yourself it’s terrible and must be changed! Of course, UI design is the area where engineers often get surprised by real-world usability tests, a system they’re convinced is terrible might work fine, or the perfect one might confuse everyone.

  56. Anonymous says:

    Maybe whats missing here is an ‘Enter’ key.

  57. Anonymous says:

    " Thinking outside the box here, why not have the GLASS SCREEN as a giant touch screen. "

    Horrible parallax problems I suspect. Even with a grid on the screen the different height of the customers would play havoc.

  58. Anonymous says:

    Not that it in any way invalidates Raymond’s point, but if you look at the ‘enlarged’ image of that vending machine, it does actually have a ’10’ button…

  59. Anonymous says:

    It does have a "10" button, but many (most?) people look for the "1" first, and press it before realizing that there’s no "0".

  60. Anonymous says:

    Just have people enter the dollar amount.

    And once they’ve entered enough cash, all those eligible items would lit up then they can use arrow key to browse to the item they want and enter.

    Problems might arise when an arrow key’s stuck and it becomes one of those gambling machines; which I suppose is rather entertaining too….

  61. Anonymous says:

    Another theme: What about people with disabilities? Will they be able to use that UI?

  62. Anonymous says:

    This reminds me of a horrible UI on parking-meters here in DK. There was a slot for coins and two buttons: One for getting your ticket and one for cancelling thus getting your deposited coins back.

    Several times I witnessed people inputting coins for just seconds later to press the cancel-button not understanding why they didn’t get the ticket.. Why..? ‘Cancel’ was a black button, ‘Execute’ was a red button…

    The new machines has a green ‘Execute’-button….

  63. Anonymous says:

    Norm’s idea works. When I was in college most of ours had an Enter key so you put the whole code in, then pressed Enter.

  64. Anonymous says:

    Like others have said, do what (most) coke machines I have seen have.

    Just have a seperate button for each product with a product picture on it.

    e.g. one button for salt & vinegar chips

    or one button for whatever flavor of chewing gum

    or whatever else.

    Easily usable by anyone and totally avoids international issues. (one is assuming anyone who wants a particular item knows what it looks like)

  65. Anonymous says:

    Such as:

    AA, AB, AC …

    BA, BB, BC …

    No more problems. :-)

  66. Anonymous says:

    Fogot to mention that you can save at least 10 number keys on the machine with my solution above.

  67. Anonymous says:

    Is this all that common? Every vending machine related fatality I’ve heard about has been from trying to get free stuff, which, when you think about it, isn’t really that big a deal.

    About 5-10 idiots are killed every year in this way… Vending machines are doing their part… are you doing yours?

  68. Anonymous says:

    Theres one of those RoboQuencher machines at my local bus station. I was really surprise when I first saw it working. Kinda made me want to buy something else just so I could watch the robot arm move around again.

  69. Anonymous says:

    John-

    "Additionally, my experience is that some people just don’t get directional pads. My father is hopeless when it comes to menus, whether they’re on games, stereos, or even DVDs."

    that’s true… but you’d agree that there are many places where this would be something everyone would love (i.e. companies related to computer business)

    …and it doesn’t have to be robot hand as such… here we have some vending machines that when you select the product, there’s a little "elevator" that goes to the line where you selected the product so it doesn’t get dropped all the way to the bottom (drinks), the "elevator" then goes down to where you can pick it up

    the same concept could be used to actually pick the product

  70. Anonymous says:

    " Like others have said, do what (most) coke machines I have seen have.

    Just have a seperate button for each product with a product picture on it."

    I don’t think this would scale well. It works for drinks machines because they generally offer a fairly small range (say < 10 products), so you can have a few fairly large buttons in a compact area.

    The sort of snack machines we’re talking about here offer 50 or more products. That many buttons of a decent size would probably occupy a good chunk of the front of the machine (I’m assuming this isn’t acceptable since retaining the big glass window is a requirement).

  71. Anonymous says:

    Some product code should be avoided.

  72. Anonymous says:

    well at a vending machine at my school,they have bags of chips in the corkscrew, when you choose a selection,it pushes the bag of chips up instead of out, and the corkscrew keeps rolling untill you get 2 bags of chips for the prce of 1

  73. Anonymous says:

    Following on the latest meme, I&rsquo;m going to link to a page talking about vending machines.

  74. Anonymous says:

    Probably not much more expensive to have a paddle (like those used in Pong), or a joystick, and a LED that lights up against the selected item. Personally I prefer the paddle, as

    a) it obeys the rule of reversibility: you can undo what you have done (as like on analog devices)

    b) it can give both a coarse and sensitive response, much like mouse acceleration.

  75. Anonymous says:

    The best way we should address this issue of wrongful sale is to replace the entire code entry system with a full QWERTY keyboard, with which the full name of the desired product is entered into the machine. Or better yet, equip each machine with a friendly midget that can get the right product, and bypass the entire computer system altogether.

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