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.

