The ‘full’ refers to the time of the full moon and the ‘change’ to the time of new or ‘changing’ moon. The time of High Water bears a constant relationship to the full and new moons at any particular place, and if you know the time of high tide after full moon you will know it for every subsequent full moon through the year. Still, you don’t really care, do you, because you get a free tide table from your chandler, or your club, or perhaps even from your bank.