With vertical line(Oy) snapping you can set a vertical lines relation for a regular line you are about to place. After you activate the vertical line(Oy) snapping mode for the line you are drawing, the line is snapped parallel to the y-axis.
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 Possible object/part modes where Vertical Lines(Oy) snapping can be used:  | 
 Regular lines.  | 
To use vertical line(Oy) snapping
. The line you are drawing is snapped parallel to the y-axis.