Click here to purchase the entire book in PDF format. Other Bases This chapter only describes 3 different numbering systems, base 10, base 2 and base 16, but there are lots of others - even some that used to be used, that aren't anymore, but still have vestigages hidden in our language. American readers should recognize the phrase ``Four score and seven years ago'' meaning ``4 * 20 + 7 years ago'' or ``87 years ago.'' This is a leftover from the days when years were grouped into ``scores.'' 1 score = 20 years, so we were working in base 20. The concept of a week is a form of base 7. Three weeks is 3 * 7 = 21 days (in other words, the number 3 is in the ``seven's'' place). Twelve inches in a foot (base 12), Fourteen pounds in a stone (base 14), Twelve eggs in a dozen (base 12), Three feet in a yard (base 3). Eight furlongs in a mile, 24 hours in a day, 60 seconds in a minute... We use these strange systems all the time without even really knowing it.