The value S′ is derived from the raw alignment score S in which the statistical properties of the scoring system used have been taken into account. By normalizing a raw score using the formula:

a “bit score” S′ is attained, which has a standard set of units, and where K and lambda are the statistical parameters of the scoring system. Because bit scores have been normalized with respect to the scoring system, they can be used to compare alignment scores from different searches.