On Thu, 01 Aug 2013 08:08:06 +0100, Nightjar wrote:

The multiplicity of codes meant that none of the keys on the common door
pad would show signs of more use than others.

And the wear/clean buttons problem can be avoided by having a nixie
tube behind each button and moving the numbers about after each use.
Also makes shoulder surfing harder.

I bet the draw back is that as people can't remember and use the the
pattern for the code rather than the code itself, codes (unless
strictly controlled) become simple...

--
Cheers
Dave.