EN
The article attempts to prove that reliable estimates in the extrapolation parametric functional size measurement methods of software development and implementation with customization projects require using benchmarking data. Accurate data for projects under consideration enable to obtain both rough estimates at the early stages of estimation process as well as more detailed estimates, in case of which one takes into account attributes of the undertaken project and differences in the productivity being characteristic of various project teams. An exemplary repository of benchmarking data allowing to derive reliable estimates with the use of extrapolation parametric FSMM of software development and implementation with customization projects is presented. Various purposes for using such data and exemplary regularities resulting from the analysis of these data are discussed.