[GreenKeys] Why and When 7.00 vs. 7.42 unit code?

[Jim Haynes]

On Wed, 12 Mar 2014, Don Robert House wrote:
> I am planning on unbinding and scanning an old Bell Publication on Telegraph 
> transmission that is also an excellent source for answers.
>
Something that is out there on the net is a scan of the AT&T Long Lines 
book "Principles of Electricity Applied to Telephone and Telegraph Work"
which has quite a bit about telegraph transmission.  Google turned up
the 1953 edition at

long-lines.net/sources/att_principles_ocr.pdf‎

and there are probably other editions also available.