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					Datum Line ja Boxing System kehyksen mitoituksessa

DATUM LINE:
Datum line system was introduced by Cole & Blackburn in 1935. The datum line is situated
midway between the horizontal tangents to the upper and lower edge of the lens shape. This
system was enshrined in BS 3199 of 1960. However, with the introduction of BS 3521 in 1991,
datum system ceased to be used in United Kingdom replaced by boxed system. Most
countries now use boxed lens system, and it is most likely that this system will be universal.

                                   Datum Line System




                                        Boxing System




BOXING SYSTEM:
It was American Optical Manufacturers Association in the year 1961 introduced Boxing System
for Lens and Frame measurements. This system is based on the rectangle formed by the
horizontal and vertical lines (vertical line is mentioned here,but not in datum system) tangential to
the extremes of each lens, by which dimension of a front (I don't use term frame) and the location
of the lenses in the front may be measured. Accordingly, HCL should be used for centration
purposes and to specify the segment top position (height) and the fitting cross height.
Again I say,effective diameter=boxed lens size,because both are the one and the same boxing
system! Therefore,Boxing System is improved version of Datum System


              Tekstin lähde: http://www.optiboard.com/forums/archive/index.php/t-1835.html (7.3.2006)   hp06

				
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