Navionics

I recently purchased a boat with a pair of G120/GPM400 MFDs, which had a Navionics card for another part of the US. I bought a Platinum CF card and put it into the master GPM-400, and I'd like to know if there is a way to verify that the GPM is using the charts from the card. It's hard to see a difference between the embedded charts and the new ones, if they're being used.

Thanks,

Josh