if you press a letter and control, it generates the control character in the left-hand column.
the letters in the third column are A = 1, B = 2 etc: 40h + the position in the alphabet.
Awesome to see ^@ as null and laying it out this way makes it easier to see ^L (form-feed, as the article says: control-L will clear your terminal screen), ^G (bell), ^D, ^C etc etc
This is so that control characters (and shifted characters — see https://en.wikipedia.org/wiki/Bit-paired_keyboard) could be generated electromechanically. Remember a teletype of the era (e.g. Model 33) has no processing power.
the letters in the third column are A = 1, B = 2 etc: 40h + the position in the alphabet.
Awesome to see ^@ as null and laying it out this way makes it easier to see ^L (form-feed, as the article says: control-L will clear your terminal screen), ^G (bell), ^D, ^C etc etc