Really struggling with this one. At first I thought ‘zigzag’ meant proceed from cell to cell going down one diagonally to cell SW or SE of previous cell. That seems the most literal interpretation of the preamble. But it was soon evident this didn’t work for the answers I’d solved.
Next thought ‘zigzag’ meant one cell to left or right then one down then next cell to left or right and so on.
Now I’m not sure of that and suspect ‘zigzag’ means wander around anyhow as long as you don’t go upwards.
This really is the most imprecise start to a preamble I’ve seen in the Listener.
Any guidance from those well past my uncertainty would be most welcome.