N unit definition

N-unit

a unit in terms of which refractivity is expressed Example: If the refractivity index n is such that: 10⁶ (n-1) = 350, the refractivity is 350 N-units, or N =350.
Found on http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=705-05-11

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