when the assembly undergo changes then the initial version number will be changed. when subprogram logic is changed then change Revision number of the version. when new subprogram is added change the Build number of the version. when the interface names i.e subprogram names, class names and the interface names are changed then change the Minor number of the version.
when new classes are added into the assembly then change the Major number of the version.
i.e Major.Minor.Build.Revision is the format followed in assembly versioning format.