

Abacus: The Art of Calculating with Beads
http://www.ee.ryerson.ca/~elf/abacus/
One particular use for the abacus is teaching children simple mathematics and especially multiplication; the abacus is an excellent substitute for rote memorization of multiplication tables, a particularily detestable task for young children. The abacus is also an excellent tool for teaching other base numbering systems since it easily adapts itself to any base.
The enduring interest in this ancient device is evident by ever increasing number of visitors to these pages from all around the world.
Patterns in Oriental carpets are never quite what you expect  a surprise here, a flourish there, a change of color, the flip or rotation of a design where you might not predict it. The more you look, the more variations you will find.
How can we explain this phenomenon? Is it the result of human choice, or human error?
The study of symmetry offers one approach to analyzing patterns in Oriental carpets. Through symmetry analysis we may identify areas of pattern that exhibit expected repetitions, and areas that vary from that expectation.



