Maybe...
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I remember my classes of math and physics, which were in French language, we used the value "n" as a designated or arbitrary amount. While in the Anglo-Saxon world, people will state "I owe you "x" number of dollars", a French language mathematician or physicist would say "I owe you "n" number of dollars"... maybe in an English language math of physics classroom lecture, the "n" is used as well as the French do, to designate a "number"...
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With jet engines, the 100% "N" value is rather arbitrary. Some engine manufacturers might decide to call the maximum rated RPM as 100%, while others will decide the maximum RPM as 98.5% or 101.2%... then like the examples for N1, N2 and N3 (of the RB211) given in previous postings, but might not be the maximum or continuous RPM values...
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We are all familiar with engine stations designations, such as "Pt-2" or "Tt-7" as pressure or temperature values for various "stations" from inlet to exhaust of engines, "N" is another conventional engineering value, expressing RPM...
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This is my interpretation of what "N" means. On the J-85, the RPM indicator was simply called RPM, not "N1", as there was only one shaft. Since I made a major clean-up of my old manuals, for "paper recycling" some years ago, no idea as to where or what publication I can refer to.
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Happy contrails