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Is Morse code without spaces uniquely decipherable?

Discusses how Morse code isn't very clear without the third (usually) unseen element, the space.

Is there a (historical?) human-optimised (vs. say, ascii or something) binary (on vs. off) code for transmitting information?

After sleeping on it, I recall one code used by Vietnam-era POWs, based on a 5x5 grid reference, optimised for decoding/learning (alphabetical order) vs. optimised for use. But, I'm not sure that it didn't also use spaces.

From history/pre-computer: ie: I don't really want to hear ASCII, or machine language - very few people (excludng Seymour Cray) can do that in their head.

Human-optimized: something that's designed around human/language foibles, ie: Morse is intended to have the fewest keys for the most used characters.

History has decided this is not a history question:

https://history.stackexchange.com/questions/17531/morse-code-is-a-ternary-human-optimised-code-is-there-a-binary-non-machine-opt

Suggestions:

T.E.D. suggests smoke signals, but uses an example in which both the question, and the answers are pre-known:

There's the smoke signal that the Vatican Council uses to communicate when they are voting. Black smoke means they haven't elected a new Pope yet, and white smoke means they have. I'd imagine a lot of other smoke signal systems can be thought of a binary communications as well, as the medium has many similarities to telegraph.

However, smoke signals in general sound intriguing. Does anyone have any references? Wikipedia mentions "Polybius square" which was the basis for the POW communication mentioned above. Knock or tap codes are another name for them.

Thanks T.E.D. for indirectly pointing me to a place (Thanks Wikipedia) to find the name(s) for one answer to the question.

March Ho suggests:

http://en.wikipedia.org/wiki/Braille , in its various language formats, is a binary human-optimised code. http://en.wikipedia.org/wiki/Night_writing , Braille's precursor, also fits your description request. Both codes are fixed-length, and therefore do not suffer from the problem as quoted in
the question.

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    But where's the computer science? – David Richerby Dec 14 '14 at 00:40
  • That was what I asked them. If this isn't CS, and it's not History, what type of question is it? I'll take it there, as soon as I figure out where there is. – user25801 Dec 14 '14 at 03:16
  • I'm not sure. Some questions just aren't on-topic anywhere on SE. [hsm.se] might be the place but I'd strongly recommend that, instead of just posting there, you post a link to this question on their meta site and ask them if it would be on-topic, first. – David Richerby Dec 14 '14 at 10:39
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    Morse code can also be seen as a binary code: There is a fundamental time unit, and in each time unit there either is signal (1), or there is no signal (0). There's a special rule that the number of consecutive equal symbols must be $2^n-1$, where $n$ is at most $2$ for the symbol 1 and at most $3$ for the symbol 0. – celtschk Dec 14 '14 at 12:45

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