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The ITU's International Morse Code recommendation ITU-R M.1677-1 specifies a "Full stop (period)" as ".−.−.−", however it falls short of specifying a decimal point. Even the examples, though they illustrate fractional numbers, don't show decimal usage.

ITU's Phonetic Alphabet and Figures regulations (AP14), however, define a "Decimal point" and require it to be spoken as "DAY-SEE-MAL".

What then is the decimal in Morse code, and where is it defined?

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In the International Code of Signals (an International system of maritime communication, including radiotelegraphy), AAA (over-bar) is designated for both full stop and for decimal point. (See flashing light procedure signaling, page 20.)

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    $\begingroup$ And this makes complete sense, because the decimal and period (aka full stop) have been the same on typewriter keyboards since the invention of the machine (not long after the telegraph), and in printing since the advent of hand-set type (17th century). You distinguish between them by context, just as with handwriting or in print. $\endgroup$ – Zeiss Ikon Aug 31 at 16:15
  • $\begingroup$ From wikipedia searches: International Morse code was proposed circa 1848 (Hamburg) and codified Internationally circa 1865. The Sholes and Glidden typewriter was first marketed circa 1874. So the code preceded the typewriter keyboard (as we now know it). However: Gutenburg circa 1450. Have to check to see if any early printings included decimal numbers (when were these popularized?). $\endgroup$ – hotpaw2 Aug 31 at 16:22
  • $\begingroup$ Napier (discoverer of the idea of logarithms) is reported to have first used the full stop or period as a numeric decimal point circa 1614 and 1619. $\endgroup$ – hotpaw2 Aug 31 at 16:30
  • $\begingroup$ Okay, wrong on the source, but right on the century for origin of the full stop as decimal divider. $\endgroup$ – Zeiss Ikon Aug 31 at 16:56
  • $\begingroup$ Can we use this in Amateur Radio? $\endgroup$ – Amin Shah Gilani Sep 1 at 0:27
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The web sites of Kent Morse Keys and of the AC6V reference compendium document use of the Morse letter 'R' (dit-dah-dit) as an abbreviation for 'decimal point.' 'R' can have other meanings, of course, but I have used and heard it used to represent a decimal point in numbers - particularly when specifying a frequency - for 50 years.

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    $\begingroup$ Interesting! I wonder if there's any historical explanation/mnemonic there? $\endgroup$ – natevw - AF7TB Sep 4 at 0:12

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