A part iteration is the smallest increment of change saved by Windchill. It is the amount of change that occurs between successive check-out and check-in operations (that is, the changes made in one editing cycle). Viewing successive iterations shows the progress made during a design project and the length of time over which modifications were made. The following diagram illustrates the iteration cycle:

When a part is created, the common part information and information unique to the first part version are saved in the database. The part is created in a modifiable state such as In Work, the initial revision is A, and the initial iteration is 1. Users must perform a check-out operation to reserve the part for editing. A part that is checked out is locked and cannot be edited by any other user. The editing user then makes modifications to the part version and performs a check-in operation when changes are complete. At the time the part is checked in, the part iteration number is advanced by one (for example, the version advances from A.1 to A.2) and the part is unlocked so that it can be checked out by other users. The check-out, check-in cycle is repeated and the iterations are saved until design modifications are complete.