Chris_D - 1:07 am on Apr 14, 2004 (gmt 0)

Why seven? Over many, many years phsychological tests show that seven is the "break" spot for memory. People can easily and accurately repeat lists of words or numbers when there are seven or fewer. The minute you hit eight, the error rate spikes. The human mind tends towqard groups of seven -- don't know why exactly, but it's definitely true.

Exactly why local telephone numbers were only ever 6 or 7 digits max in the old days. A few years back (here in Australia) to expand number capacity, they went to 8 digit numbers. So they added the numeral '9' infront of the old seven digit number - so most people actually remember the number as a seven digit phone number - with a 9 in front of it....