Re: Automated Vending/Ticket Machines

Subject: Re: Automated Vending/Ticket Machines
From: Peter Neilson <neilson -at- alltel -dot- net>
To: "TECHWR-L" <techwr-l -at- lists -dot- raycomm -dot- com>
Date: Sat, 06 Dec 2003 19:58:11 -0500


Test, test, test, and retest. The audience is everyone from certifiable
lunatics to certified software designers. A good interface will not
mislead anyone, at least not much. The hardest part will likely be
having to change a sequence of events that has already been decided,
for which your colleague is expected merely to provide text.

The US Post Office has provided some exemplary wretched interfaces in
the design of its stamp vending machines. They are better now, but if
you tried using one of them maybe five or ten years ago you know what
I mean. I've purged my mind of the details, but they were awwwful!

It is crucial for the design to handle "pushing the wrong button" in
the right way. Here are some BAAAAAAADD ways to treat a wrong button:

- "We don't have to worry about that. No one will make that selection
because it doesn't mean anything."

- Display "USER ERROR". (Fails to say what user should have done instead.)

- Return to previous screen.

- Make a beeping noise. (Some customers cannot hear it.)

That's a short list. There is no end to the possible wrong things that
can be designed in.

At this time the system should already have a state-machine description
that is still modifiable. A state machine is a description of every state
that the machine can have and the rules for getting from one state to
another, and the side effects (in this case the displayed text). Here
is a simple state machine:

STATE 1: WAITING FOR COIN. Inserting coin effects transition to STATE 2.

STATE 2: VALID COIN? If coin is a quarter (25 cent piece) go to STATE 3.
Otherwise go to STATE 4.

STATE 3: DISPENSE. Side effect: dispense candy. Go to STATE 1.

STATE 4: WRONG COIN. Side effect: return coin. Go to STATE 1.

Note that this is NOT a computer program. It is a set of machine states,
intended to be a complete description of a candy-vending machine, whether
mechanical or electrical, or anything else. The astute observer will
see that a few states have been overlooked, for instance CANDY EMPTY
(the description above simply steals the money), COIN JAMMED, and all
the states for accepting combinations of coins and for making change.

On Fri, 05 Dec 2003 21:15:58 -0800, Denise Cusano <denisecusano -at- usa -dot- net> wrote:


Greetings Whirlers,

I am helping a colleague gather some information. She is working on a project
for a transit agency. They are putting in automated
ticket vending machines with a CRT touch screen user interface, and she wants
to help them develop a good script for the screens.

Does anyone know of any good studies or "best practices" reviews about
developing friendly, usable screen prompt sequences for people using
automated vending machines (or any step by step thing, like on the web,
where it branches based on customer choices)?

I've searched the archives, but only came up with a thread on basic
terminology.


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References:
Automated Vending/Ticket Machines: From: Denise Cusano

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