fudge factor

from WordNet (r) 3.0 (2006)

fudge factor
    n 1: a quantity that is added or subtracted in order to increase
         the accuracy of a scientific measure [syn: {correction},
         {fudge factor}]

from The Collaborative International Dictionary of English v.0.48

fudge factor \fudge factor\, n.
   a term or factor inserted into a calculation to compensate
   for anticipated errors, or to arbitrarily make the result
   conform to some desired conclusion.
   [PJC]

from Jargon File (4.4.4, 14 Aug 2003)

fudge factor
 n.

   [common] A value or parameter that is varied in an ad hoc way to
   produce the desired result. The terms tolerance and {slop} are also
   used, though these usually indicate a one-sided leeway, such as a
   buffer that is made larger than necessary because one isn't sure
   exactly how large it needs to be, and it is better to waste a little
   space than to lose completely for not having enough. A fudge factor,
   on the other hand, can often be tweaked in more than one direction. A
   good example is the fuzz typically allowed in floating-point
   calculations: two numbers being compared for equality must be allowed
   to differ by a small amount; if that amount is too small, a
   computation may never terminate, while if it is too large, results
   will be needlessly inaccurate. Fudge factors are frequently adjusted
   incorrectly by programmers who don't fully understand their import.
   See also {coefficient of X}.

from The Free On-line Dictionary of Computing (8 July 2008)

fudge factor

   A value or parameter that is varied in an ad hoc way to
   produce the desired result.  The terms "tolerance" and {slop}
   are also used, though these usually indicate a one-sided
   leeway, such as a buffer that is made larger than necessary
   because one isn't sure exactly how large it needs to be, and
   it is better to waste a little space than to lose completely
   for not having enough.  A fudge factor, on the other hand, can
   often be tweaked in more than one direction.  A good example
   is the "fuzz" typically allowed in {floating-point}
   calculations: two numbers being compared for equality must be
   allowed to differ by a small amount; if that amount is too
   small, a computation may never terminate, while if it is too
   large, results will be needlessly inaccurate.  Fudge factors
   are frequently adjusted incorrectly by programmers who don't
   fully understand their import.