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Alpha Rule
(lemmy.ohaa.xyz)
Be sure to follow the rule before you head out.
Rule: You must post before you leave.
In an 1895 paper, Röntgen used "X" to label an unknown type of radiation. And the name stuck, despite his later objections. (Some languages do call them Röntgen rays.)
German for example does this.
Ix-Strahlung certainly doesn't roll off the tongue.