There are two main ones 1. modern navigation systems often work in true North already but have to map to magnetic for display & to match charts. 2. magnetic

There are two main ones 1. modern navigation systems often work in true North already but have to map to magnetic for display & to match charts. 2. magnetic north moves! This greatly complicates how you deal with the first point. I don’t envy the Canadian pilots they were talking about who tested some of this current stuff, and found their plane’s idea of the runway direction way very different from where it lay.