Buzz
I am going back forty years to when I used such equipment. In those days we only used 64 codes (00 - 77 octal) not the present 4096. It was possible to dial in a code on the radar console and any aircraft squawking that code would be marked with a slash close to the primary radar return. Squawking Ident produced a second slash.
It was possible to view the actual code as a series of slashes or blanks between two lines called framing pulses. These slashes were very close together so good eyesight was required to read the code in this way.
These slashes were actually binary bits in two groups of 3.
The bits represent the values 1, 2 and 4 which, when added together can represent the numbers 0 - 7 depending which bits are on or off i.e. eight values (Octal)
It was a bit like reading a bar code as found on almost everything today.
The slashes could be read as follows. (- below means off i.e. invisible)
- - - equals 0
- - | equals 1
- | - equals 2
- | | equals 3
| - - equals 4
| - | equals 5
| | - equals 6
| | | equals 7
So the code 65 would look a bit like this ( the square brackets [] are the framing pulses.
[||- |-|]
I hope that this makes it as clear as mud!
Reg Ford