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Explanation: OK was long thought to originate from "O Killed" in action, a military abbreviation from early 19th century. Whether or not this etymology is right, it still corresponds very well to the military "RAS" in French. Furthermore, it's an expression everyone understands, whereas you have to guess what "NTR" means. I've never seen it, anyway, in 20 years of military and industrial translation. I've also heard and used "Check", but verbally only. Why look for an expression that is difficult to understand when you have the convenience of "OK"?