A normalized measure of software size, roughly equivalent to writing a line of code. To compare projects sized in different function units in a meaningful way, it is necessary to identify the smallest common unit of size. Without this common reference point, it would be impossible to compare projects sized in Stories or Use Cases with projects sized in Function Points, as there would be no way to determine their size relative to each other. The default name for the Base Size Unit is Implementation Units, (IUs), but it can be renamed by the Site Administrator.
When the primary size record for the project is captured using a function unit with a gearing factor > 1, a normalized size record will be calculated to translate the size record into equivalent Base Size Units. If the primary size record counts are already in the Base Size Unit, no normalization is needed. The gearing factor for the Base Size Unit is always equal to one and cannot be changed.