Hi :) , That might not be clear, even for developer, and even less for a librarian. How could this info be delivered reliably to the user? To avoid running in circle during too long before realizing that? Even more hard to understand when there are cases like biannual where if you start from February, it will work even if you assumed that January was 1. But if you start from February, there will be issues after one year. Should there be tooltips? The related fields are marked with a red dot in the following screenshot. https://framapic.org/4P2ZzbgJpuvA/SIleKzEuYVaG.png Cheers, -- Victor Grousset, dev support/maintenance BibLibre, Services en logiciels libres pour les bibliothèques BibLibre, Libre/Open Source software and services for libraries