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The Numdrum was invented by John Harrison to help children struggling with the basics of understanding numbers, adding and subtraction. It is a simple but revolutionary development, which through its design addresses the serious inadequacies of some present teaching aids, most notably the number square.
The numdrum is a number line extending from 0-139, which has been given a decimal structure by winding it round a tube in helical form in such a way that there are 10 numbers per turn. This makes the number line continuous, unlike a 100 number square. The surface is dry-wipe and it is accompanied by a manoeuverable plastic sleeve and an A4 sheet of suggested uses and puzzles to solve.
Just as important, children find it fun and interesting to use!