| Definition: | smallest contrast, produced at the eye of an observer by a given object, which renders the object perceptible against a given background Note 1 to entry: For meteorological observations, the object has to be rendered recognizable, and hence a higher threshold is to be expected. The value of 0,05 has been adopted as the basis for the measurement of meteorological optical range. Note 2 to entry: This entry was numbered 845-11-21 in IEC 60050-845:1987.
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