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'Arrow Arithmetic 2' printed from http://nrich.maths.org/
One good way to realise a twizzle as a manipulative is with a piece
of elastic. You need to mark 3 spots on the elastic - say a black
spot for the origin, a blue spot for the end of the unit arrow, and
a red spot for the end of the number arrow.
Make a few of these elastic twizzles up, and see if you can use
them to do simple calculations.