First, create two (or more) Bill of Materials on the same product.
Then, open the first Bill of Materials, and launch the wizard with `Action / Compare Bill of Materials`.
In the `BoM v2` field, select a BoM to compare against the current one,
and click on `Compare`. The result of the comparaison is returned as
a PDF report with three sections:

- products updated
- products added
- products removed