Reference surface centre definition

reference surface centre

for a cross section of an optical fibre it is the centre of that circle which best fits the reference surface NOTE 1 - The reference surface centre may not be the same as the core centre and the cladding centre. NOTE 2 - The method of best fitting has to be specified.
Found on http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=731-02-26

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