Off-topic: Magic Number 7 (WAS: Re: XML Editors - Word 2000??)

John E. Simpson simpson at
Fri Jul 2 14:30:20 BST 1999

At 10:23 AM 7/2/1999 +0100, Philip Nye wrote:
>Rick Jelliffe wrote:
>> 1) you have to remember the name, this is difficult if there are more
>> than 7 names in frequent use;
>> 2) if there are more than 7 elements at any one level, there is a
>> selection 
>> problem for GUIs: style provides a way to key hierarchy that provides
>> reinforcing feedback;
>Incidentally, where does the magic number 7 come from?

When I was at AT&T years ago, there was a company legend (possibly
apocryphal) about the length of US telephone numbers. According to this
legend, Bell Labs had surveyed large numbers of customers and determined
that, on average, people could remember 7 "things," plus or minus 3, about
another "thing." Ergo, a phone number would optimally be made up of: a
4-digit "main portion," sans exchange and area code; a 3-digit exchange;
and a 3-digit area code. This was supposedly in descending order of need to
remember the additional portions, assuming that you'd need primarily to
call people in your own exchange, followed by people in your area code but
outside your exchange, followed by people in other area codes.

I don't know where Rick's magic 7 comes from.

John E. Simpson          | It's no disgrace t'be poor, 
simpson at      | but it might as well be.
                         |            -- "Kin" Hubbard

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