Understanding what significant digits really mean

Raymond Chen June 16, 2006 Jun 16, 2006 06/16/06

A double-precision floating point number carries fifteen significant digits. What does this really mean? I multiplied 0.619207 by 10,000,000 and got 6192069.999999991 instead of 6192070. That's only six significant digits; where's my fifteen? Talking about significant digits is really just a shorthand for talking about relative precision. "...