Correction: Re: trivial amusement of the week...

[Richard D G Cox]

> this must be from the cockup category; I was using the postcode from:
> http://www.uk-dso.odedodea.edu/menwith/contact.html
> viz: "HG3 2RV" - which is (presumably) erroneous...

Indeed so; by definition no UK postcodes are allowed to have any of the
letters C I K M O or V in the "in-code" (the second part of the postcode).

For those curious, all zones use the same set of of 4000 possible in-codes
from 0AA to 9ZZ although not all of those possible codes are used in every
out-code area, and in some cases very few of the possible codes are used!
The exclusion of those letters is partly to reduce substitution errors
(as in 1 for I, M for N, U for V, etc) and partly to ensure that there are
no more than 4095 possible combinations to be allocated a binary coding to
store on the envelope; in the original postcode scheme there were two rows
of twelve positions, each row between outside markers, and in each of the
24 positions phosphor dots could be either absent or present: this limited
the scheme to 2**(12) possibilities for the out-code and 2**12 positions 
for the in-code: with some possibilities being set aside for whatever test
codes were considered necessary.

Of course, the mechanism used to sort letters based on the postcoding does
very neatly allow letters to specified postcodes to be sorted in different
ways from that which might be expected, while the staff who are running
the machines would have no knowledge that anything unusual was happening!

Richard