Standard refractive modulus gradient

4-1-905

Alternative term: Standard M gradient

That uniform variation of refractive modulus with height above the earth's surface which is regarded as a standard for comparison. The gradient considered as normal has a value of 0.12 M units per metre (3.6 M units per hundred feet).

Reference: C.C.I.R.

Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)

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