This unusual clock tells the time with a spiral arm. To add a little mathematical beauty, the arm is a Fibonacci spiral meaning the line moves further from the centre by a factor of 1.618... (the Golden Ratio) for every quarter turn. What about every 12th of a turn - the hours of a clock? We'll leave that up to you to work out. Check your working out by measuring the clock itself!
Dimensions: 30 x 10 cm
Takes 1 AA battery