determine change of partner at saving IBase

Hello experts,

at time of saving an IBase, I need to determine if the partner (Ship-to) has changed. This information needs to be stored in a table.

What I need:

1) I need a BAdI or UserExit that is processed at saving an IBase and where I can check if Partner Ship-to has changed

2) How do I determine if partner has been changed (I would somehow need old value and new value to compare)?

Thanks for your input.

Regards,

Elko