Well explained sir thanks

Respected sir I had a good knowledge after your lessons.can you please explain catzoc calculation and how to put in our passage plan? Suppose we are navigating from point A to B ships draft 15 mtrs and depth of water 20 mtrs point A showing 6 stars ie A1 and point B is showing 2 stars ie D both depth is showing 20 more then how to do the ECDICS settings applying CATZOC calculations.? Kindly help and guide me sir.