In article , Peter Smyth
writes
Is there a reason why the don't use numbers ending in 8 or 9?

As other posts have said, the programme machines work in binary, shown
as octal in the train numbers.

To represent a digit from 0 to 7 requires three sets of circuits.
To represent a digit from 0 to 9 requires four sets of circuits.
So the fourth circuit gives only a 20% growth in numbers for a 33%
growth in complexity.

More precisely:
Octal:
6 circuits give 64 train numbers
7 circuits give 128 train numbers
8 circuits give 256 train numbers
Decimal:
6 circuits give 40 train numbers
7 circuits give 80 train numbers
8 circuits give 100 train numbers
9 circuits give 200 train numbers

If you were designing and costing it, which would you choose?

[Note that there's no need to do arithmetic in the system, so there's no
issue with remembering that the number after 77 is 100, for example.]

--
Clive D.W. Feather, writing for himself | Home:
Tel: +44 20 8495 6138 (work) | Web: http://www.davros.org
Fax: +44 870 051 9937 | Work:
Written on my laptop; please observe the Reply-To address