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This question came up when having a pun-ridden discussion with some of my colleagues: When and why did we start using the word "analogue" to mean "not using numerical digits?"

Etymonline only has an origin for the sense of "having analogy to something else," but that's not the meaning I'm interested in. It does mention that the "computing sense" is recorded from 1946, but not what the origin of that sense is.

I can guess there may once have been a specific and well-known analogy to which this use of the word was a reference, and that that analogy has since faded from common knowledge... But an uneducated guess is just folk etymology that hasn't yet spread. As this use of the word is apparently fairly young, I'm hoping there's a more reliably accurate origin story than mine out there.

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    Since computers were not something that most individuals had contact with before the 1980's, I'd surmise that "analogue" vs. "digital" came about to differentiate types of clocks and watches - which were widely available decades earlier. (Nope, I can't prove it.) – Oldbag Apr 24 '15 at 10:44
  • @Oldbag - The term "analog", to refer to non-computer electronics, was not used until about 1980. – Hot Licks Apr 24 '15 at 10:50
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    @HotLicks - Really? Says who? – Oldbag Apr 24 '15 at 10:53
  • @Oldbag - Sez me. The need only arose when consumer digital electronics began to appear. As Maynard Wright indicates, the prior terms were "discrete" and "continuous". – Hot Licks Apr 24 '15 at 10:58
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    @Hotlicks, as an electrical engineer, my two cents is that "discrete" and "continuous" were not prior terms - they have a different meaning than (and are used in conjunction with) analog and digital. That is, for example, you can have a continuous analog signal or a discrete analog signal - they mean different things. – Brian Mar 15 '17 at 15:36
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Analogue comes from computing.

"A Chronology of Analogue Computing" article in The Rutherford Journal

The word ‘analogue’ was first used as a technical term during the 1940s, and referred specifically to a class of computing technology. Today, the word enjoys much wider usage, typically conveying continuity. For example, engineers will discuss analogue and digital signals, and musicians decide whether to record their work on analogue (continuous) or digital (discrete) media.

Analogue computing emerged during the nineteenth century and became a mainstream computing technology during the early twentieth.

The word analogue has been used because the electric signal, for example, in analogue telephone line, is transmitted in a way that the voice vibrations correspond to electric signal fluctuation. In other word, the electric signal 'imitates' the voice.

In digital transmission, voice is coded into bytes, then is decoded with special protocol.

Another example is radio vs Morse code. Radio directly (by analogy) transmits the voice with electric signal variation. Morse code transmits only combinations of dots and dashes that are decoded by a trained person. So we can call Morse message digital because the concept is the same coding and decoding rather than an electric analogy of physical phenomena.

So the word analogue is used to reflect the concept when some physical phenomenon is converted into its electric signal analogue.

The word digital is used when a phenomenon properties are coded, then decoded.

Here are a few examples and articles to explain the difference between analogue and digital concept:

The basic difference between analog and digital technology on howstuffworks.com

Analog vs. Digital with explanation and comparison chart on diffen.com

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    Interesting information, but does it tell us (with supporting references) about 'the [historical] origin of “analogue” as a term meaning “non-digital”' rather than just the reasoning behind it? – Edwin Ashworth Apr 24 '15 at 9:24
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    It doesn't have to be converted into an electric impulse analogue - it can be some other form that is analogous to the thing being represented. For instance the angle between a clock hand and the 12 mark is analogous to the time. – bdsl Apr 24 '15 at 11:45
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    @bdsl that is right, a thermometer is also called an analog device if it has scaled tube, not display, but the principle is analogy in some form, either electric voltage or hands position or thermal expansion. – alx Apr 24 '15 at 11:51
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    @user867 , analogue can not be a synonym of digital because the principle is different. A good example is punched tape that was used in old computers to transmit data to processor versus magnetic tape in tape recorders used to play back sound. Punched tape stored 0 and 1 combinations while the tape stored magnetic signal of variable intensity. Also, it is not only English that adopted this terminology, other language use similar differentiation. – alx Apr 27 '15 at 3:01
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    @Barmar, maybe you can call 'digital' 'indirect analogue'. Direct analogue devices are much dependent on the quality of signal transmittance whereas digital are only dependent on passing or not passing signals. Another interesting thing is that 'digital' technology usage is possible without electricity, like Morse code. Morse code can be transmitted with human gesture and flags from ship to shore or another ship but it uses 'digital' principle of coding and encoding signal - a combinations of dots and dashes. – alx Apr 28 '15 at 0:48
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I believe the usage of the word comes from analogue electronics.

Analogue electronics (or analog in American English) are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two levels. The term "analogue" describes the proportional relationship between a signal and a voltage or current that represents the signal. The word analogue is derived from the Greek word ανάλογος (analogos) meaning "proportional". (Wikipedia)

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    Except that "analog electronics" is something of a back-formation. At one time all electronic were analog. The term was adopted from computing. – Hot Licks Apr 24 '15 at 10:05
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    @HotLicks See here for the literature references from 1940s and 1950s using the term analog computing. – Honza Haering Apr 24 '15 at 11:37
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    @HotLicks This is not true. My uncle was an army electrical engineer who worked on America's early computers. He taught me the term in the 1960's and indicated that he had been using it since at least the 50's, and he was very explicit in it's use for non-computing devices well before the 1980's,. (specifically in communications and signaling electronics in the 50's, which is were he got his start) And the explanation that he gave was essentially identical to the one above. – RBarryYoung Apr 24 '15 at 18:11
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    @HotLicks You may have winked, but my uncle did not. And just to be clear, Teletypes and their competitors (which preceded computers) used digital signaling and was called such by engineers since at least the late 1950's. And though they could also be used with computers, they were communications devices, not computers. So, yes, there were both non-computer digital electronics before the 1980's and use of the comparison "analog vs digital" wrt to them. If you want to walk the claim back to "popular terminology", that's a different story. – RBarryYoung Apr 24 '15 at 18:35
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    @Honza Haering. Good answe, the only correct one. I will vote for it if you (a) clarify that the term was established and used decades before the digital era; that it still has the same meaning; that it means "non-digital" only to uneducated folk; and thus the Question of when it came into use as "non-digital" is irrelevant because it doesn't mean that, I will vote for it. IOT, clear up the confusion introduced by both the seeker and HotLicks. – PerformanceDBA Apr 25 '15 at 3:47
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The original electronic computers were "analog". The computations were done by adding/subtracting/integrating/differentiating electronic signals (voltages), so these signals were "analogs" of the real-life values being modeled.

(There were also various types of electromechanical computers, of course, from Babbage's "Difference Engine" to Turing's code-breaking device to several others in England and the US. The devices were incredibly slow and unreliable, though -- and noisy!)

"Digital" electronic computers (generally considered to start with the Eniac at University of Pennsylvania) were so-named to differentiate from analog ones.

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    I agree. In the late 1960s I operated a Qeleq analog computer, which was hard-wired for one job: Least-Cost Animal Feed Formulation. It contained an array of modules, one per potential feed ingredient, each itself consisting of an array of tuneable potentiometers, each representing one parameter of the ingredient - % protein, % fibre, etc. The point of 'analog' was that resistance of each 'pot' was analogous to a real-world quantity. – David Garner Apr 24 '15 at 11:10
  • This answer is incorrect for many reasons. The term existed and was used (ie. it had specific technical meaning and context) decades before the digital era. Analogue means Difference, the change in the electrical charge, hence Difference Engine clearly described the fact that it was based on the change in the charge. – PerformanceDBA Apr 25 '15 at 5:12
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    @PerformanceDBA - The Difference Engine was no more "analog" than a Marchant calculator. And analog does not mean difference, is means "something that is similar in some ways to something else". – Hot Licks Apr 25 '15 at 12:19
  • @HotLicks, agreed. 'Difference' in early computing was about generating mathematical tables. – David Garner Apr 26 '15 at 11:57
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    Here is a reference (from 1949) that supports your claim: "digital computers count numbers as the Chinese count on an abacus, while an analog computer makes believe it is itself the physical process to be studied". I could not find any reference to "analog signals", etc., until the 60s. – Oleksandr R. Sep 22 '15 at 1:51
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Earlier radio and electronics references often classified signals and/or variables as "continuous" or "discrete" as on page 981 of the Fourth Edition (1956) of "Reference Data for Radio Engineers," published by ITT.

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When the word analogue became an antonym of digital is a question that might better be reversed, since "analogue" certainly preceded "digital" as a description of means of representation. The continuous or discrete description for analogue and digital respectively is perhaps the most universal explanation of the difference in representation of data. The first instance is empiric (based on experience), the second abstractive (based on theory). This is illustrated by the fact that in an analogue recording the data stream follows a direct perception or stimulus, whereas a digital recording generates bytes based on probability. The first simply expresses a more direct causal connection to the origin of the data than the second.

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    OK, so what's the answer to my question? I already know what the words mean; I want to know how they came to have those meanings. – user867 Sep 22 '15 at 0:22
  • @user867 - This answers the question, only the answer is that your question is improperly framed. Analog came first, and when digital came along it had to differentiate itself from analog (by using "digital" instead of "analog"). – Hot Licks Sep 22 '15 at 2:28
  • @HotLicks I am aware that both of these words took on new meanings at around the same time, one in response to the other. I wish to know when and why this event occurred, and this you have not explained. Like the tennis player in the old hot air balloon joke, your answer is both technically correct and not actually useful. – user867 Sep 22 '15 at 3:58
  • @user867 - Oleksandr R has elsewhere in this thread posted comments showing a reference to analog and digital computers in 1949, with precisely the same meanings as today. That goes back to the dawn of digital computing (though analog computing goes back farther). – Hot Licks Sep 22 '15 at 11:27
  • @HotLicks If that information is an important part of the answer, it should be made a part of the answer; The SE format requires that a good answer stand alone. (Oh, but include references where attribution is appropriate.) Also, if the only part of the answer that answers the question is contained entirely within another answer, then shouldn't this answer be an upvote and a comment on that answer? – user867 Sep 22 '15 at 23:31
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Possibly from Ancient Greek prefix ἀνα- (ana-), from ἀνά (aná, “on, up, above, throughout”) and logos, loosely defined as a word (as embodying an idea), a statement, a speech...

Cf. "logic"... which opens up a whole 'nother can of worms... :)

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