Edwards, A. D. N. (1997). How hard can it be to design a hole in the wall? Interfaces (36): p. 3.
Where does the average person come into direct contact with a computer interface most often? It is surely the cash dispenser. These machines have been around for over twenty years, and their function is very simple. So why are their interfaces so badly designed? Their designers do not even display common sense, never mind HCI knowledge (at least not in the machines I use).
One of the annoying traits I have observed is their promising what they cannot deliver. The worst case was one which let me go through all the stages of specifying how much money I wanted before telling me that it was unable to dispense cash. Was there some reason why the Welcome screen did not simply say 'This machine is unable to dispense cash, but all other services are available'?
A slightly less restrictive version is in machines which offer standard amounts of cash. In other words, one can select £20, £30, £40, £50 and so on, by pressing the corresponding button. I have been in situations where I have pressed the £50 button and then the machine has told me that I can only have multiples of £20! If that is the case why offer me amounts which are not multiples? Similarly a receipt is usually offered with my cash so it is again annoying to have selected the option and then be told I cannot have the receipt.
The machine has knowledge of its current status (filled with only £20 notes, out paper in the printer or whatever). So surely it would be a trivial programming task to only offer amounts which it can dispense or not to offer receipts (perhaps with a note on the screen from which one would expect to select that option)?
Another machine allowed me to submit a request for cash (with a receipt) without having specified what amount I wanted. It eventually informed me that the amount I had entered was not a multiple of £10 but I had not entered any amount.
My latest experience is still puzzling me. I selected my usual £50 with a receipt and was given the warning 'an unusual document mix may be dispensed'. What does that mean? Might I receive lottery tickets instead of cash, a birthday card instead of my receipt? And note that the message was that I 'may' receive this unusual mix. I still don't know whether I did or not.
I haven't the time or the bank balance to keep teasing these machines to see how else they will surprise me. Perhaps other readers have other stories, but the question remains: Why are these interfaces so naive and badly designed? Designing a cash dispenser interface is the sort of project you might give to undergraduates on an HCI course, and I would penalize anyone whose design had some of the above basic flaws, so why can the professionals not do better? Cash dispensers a ubiquitous, used by large numbers of non-expert people and have been around for over 20 years. Surely their user interfaces could and should be models of good practice, not a source of HCI howlers.