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Part of being approximate is simplifying numbers.

We trade accuracy for greater convenience.
We substitute a nearby number which is easier to work with, or to remember.
We look for a number which is more convenient, but which is still close enough.

Some ways to simplify a number...

• Round it off
  Create zeros.
  So 199 becomes 200.
• Round to an order of magnitude
  Round a lot, to the nearest "power of ten".
  So 218 becomes 100, and 2,180 becomes 1,000.
• Slide the decimal point
  Compact those zeros created by rounding.
  So 200,000,000 becomes 2 x 10⁸ (exponential notation).
• Substitute a number you can remember
  Instead of rounding, find a nearby number you can remember.
  So 218 becomes 222, or 210, or 200, or something else easy.

Notes:

Doables:
  Need a discussion of "how close is close enough?".
  And ways of describing closeness [percent error, etc]
  Dimensional analysis as an extreme form of rounding.
  Quantity calculus as "simplifying"?

History:
  1998.Jul.02   Added History, Doables (mostly from Notes).
  1997.Aug.02   last change
  1997          created