Wearer of Hats, on 07 January 2013 - 06:05 AM, said:
I thought, at least for numbers in a sequence, that was about 4 or 5, which is why PINs, door codes and car registration plates are all 3-4 numbers.
Miller's law says that a person normally can retain or process only seven give or take two (7±2) items (chunks) of information in their correct serial-order, in his or her short-term (15 to 30 seconds duration) memory. However, it is accepted more as a rule of thumb than a scientifically proven fact. It's also called Miller's Magic Number.
I realize that this is again the number 7, so this might be an explanation as well. Subconsciously it was used already in the olden times,because it is the amount we are able to remember. Just another possibility I suppose.
Edited by TheSearcher, 07 January 2013 - 06:22 AM.