Left: The large rectangle is plastic and can be split into a square (blue) and two plastic rectangles (red and {green).
Centre: The two arcs drawn in each square.
Right: A Harriss spiral.
Image: Chalkdust.
More from Chalkdust
Prize crossnumber, Issue 17
Can you solve it?
On the cover: Some assembly required
Trippy brain massages from Sam Palmer's artwork on the front of Issue 16
What’s hot and what’s not, Issue 06
Mathematical fashion advice for an ever-changing world
Issue 05
Graphical linear algebra, slide rules and game theory in nature. Plus all your favourite fun pages in our spring 2017 issue.
Switching sides in a matrix equation
Looking for a neat description of this useful matrix part-inverse
Introducing the Cuboku
Can you solve our 3D Sudoku puzzles?