"@" being the code immediately before "A" in the ASCII character set. For convenience, some terminals accept Ctrl-Space as an alias for Ctrl-@. In either case, this produces one of the 32 ASCII control codes between 0 and 31. Neither approach works to produce the DEL character because of its special location in the table and its value (code 127₁₀), Ctrl-? is sometimes used for this character.

When the control key is held down, letter keys produce the same control characters regardless of the state of the shift