Just to add some more confusing info, you can’t really get to the calculated or plated GCM if you’re towing a caravan and you use the recommended 10% towball mass.
The reason for this is that the unhitched van can’t weigh more than the towing capacity.

Example with my Patrol with a GVM of 3550 kg and towing capacity of 2500 kg.
I load my Patrol to 3300 kg and hitch up my 2500 kg van. The 250 kg towball mass brings the Patrol to its allowed GVM.
The van now only has a GTM of 2250 kg so the total combination weight that will show on the weighbridge is 5800 kg with both at max allowed load so I can’t reach my plated GCM of 6050 kg.

Hope that makes sense..