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
Mapmatics
We review the third of this year’s nominees for Book of the Year
Chalkdust Book of the Year 2022
We announce the shortlist of our favourite maths-themed books of last year
Somewhere over the critical line
Read about Maxamillion Polignac's adventures in a prime-hating world
Top ten vote issue 05
Vote for your favourite geometry instrument
Victorian maths tricks with old money
Exploring mental arithmetic tricks in T. Martin's 1842 guide, 'Pounds, shillings and pence'
Do you have too many or too few friends?
Do we have a natural limitation on the number of friends that we have?