what is 21 indicate

[nitis...@gmail.com]

Hi,

I have a question about what is happening in this video at 00:27:33 -

http://www.youtube.com/watch?v=9wNFZ0EVXi4#t=1653s.

what implies 21, why you are using it the perpendicular to y-axis and not in x or z.

Thanks!

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Reference Key - Key('StudentQuestionEntity', 4888530265309184, namespace='ns_noc21_cy33')

[Angshuman Roy Choudhury]

2subscript1 indicates a screw axis, which produces a rotation of 180 degrees and a translation of 1/2 unit along the direction of the screw movement. This can be along the X, or Y or Z axis. In case of a monoclinic system, where Y is the unique axis, this 2(1) screw is along the Y axis.