math error in old air traffic control book

[Don Shepherd]

From the book "Air Traffic Control: The Uncrowded Sky" by Glen Gilbert (an ATC classic). The book is from 1973, but even then transponder codes were 4-digit octal numbers. 1029 would not have been possible.

Perhaps HP saw this in 1974 and therefore allowed 0-9 in octal -> decimal conversions on the HP-65!

[Maximilian Hohmann]

Hello!

(05-13-2019 11:34 PM)Don Shepherd Wrote:  The book is from 1973, but even then transponder codes were 4-digit octal numbers. 1029 would not have been possible

An esay to make mistake... Among other things I teach instrument flying and with students in the simulator one needs to take the part as air traffic controller also. So in order to give them something different from the usual "Sqawk 1234" from time to time, I often (more often than not...) give them "impossible" codes which can not be dialled into the transponder by mistake. Sometimes on of them will say: "There is something wrong with this unit - it won't accept the number you gave us" showing me that they must have slept through their ground course :-)

Regards
Max

[KeithB]

Octal confusion must have been a surprisingly common problem. In my 2nd edition of K&R, they have the following in the "Summary of Changes" from the first to second edition:
"Everyone's favorite trivial change: 8 and 9 are not octal digits"