Flipping 1

 Q Sometimes you flip lines, or shapes, horizontally or vertically - why?

 A It results in a different symmetrical pattern (see more under tessellations menu). For example, in DIY line example 1, instead of just rotating the second line, let's flip it horizontally too. Note the markers a & b.

It looks nearly the same in this case as the line, by chance, is almost symmetrical but now...