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In 1927 the International Radio Consultative Committee or CCIR was formed (which would later become the ITU-R).  In their first meeting in 1929 in The Hague they decided on how to classify "Hertzian waves" according to their frequency(([[https://babel.hathitrust.org/cgi/pt?id=mdp.39015064383717&seq=112|International technical consulting committee on radio communications, first meeting, The Hague, September 19-October 2, 1929

]] opinion 6 - page 100)).  It classifies them into:
| Ultra-short waves | Frequencies exceeding 4,000 kc/s (waves below 75 meters) |
| Short waves | Frequencies exceeding 4,000 kc/s and 550 kc/s (waves from 75 meters to 545 meters) |
| Mean waves | Frequencies between 550 kc/s and 40kc/s (waves from 545 to 7,500 meters) |
| Long waves | Frequencies between 40kc/s and 10kc/s (waves from 7,500 meters to 80,000 meters) |

With mean waves being up to 7,500 meters, since that is around the wavelength that intercontenental and transcontinental traffic is separated.  The limit of 80,000 meters is due to the previous Washington Convention (( [[https://rsgb.org/main/files/2018/09/1927-Radio-Regulations.pdf|INTERNATIONAL CONVENTION OF
RADIOTELEGRAPH WASHINGTON, 1927. INTERNATIONAL RADIOTELEGRAPH CONVENTION AND GENERAL AND SUPPLEMENTARY REGULATIONS.]] )) from 1927.  

Then in the third meeting of the CCIR in 1937(([[https://babel.hathitrust.org/cgi/pt?id=osu.32435056937899&seq=112|International radio consulting committee (C.C.I.R.) : fourth meeting, Bucharest, May 21-June 8, 1937 ; report of the Delegation of the United States of America and appended documents no.41 1939]] opinion 85 - coincidentally, also page 100)), says that "did not strictly and fully take effect and had several disadvantages for practical usage" and "that metric classification holds several advantages" comes up with:

^ Designation according to length ^ wavelength in meters ^ designation according to frequency ^ frequency in kilocycles per second ^
| Myriametric                     | Above 10,000         | Very Low                           | Below 30 |
| Kilometric                      | 10,000 to 1,000      | Low                                | 30 to 300 |
| Hectometric                     | 1,000 to 100         | Intermediate                       | 300 to 3,000 |
| Decametric                      | 100 to 10            | High                               | 3,000 to 30,000 |
| Metric                          | 10 to 1              | Very high                          | 30,000 to 300,000 |
| Decimetric                      | 1 to 0.1             | Ultra high                         | 300,000 to 3,000,000 |
| Centimetric                     | 0.1 to 0.01          | Super                              | 3,000,000 to 30,000,000 |