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. See also coefficient of X.