Using the average measurement (i.e underbust plus fullest part of bust, then that answer divided by two) I think would be the most effective, as this is how most websites selling binders measure size. A lot of people, me included, have problems by being between two sizes, therefore, having this as the standard way of expressing chest size on here would, in my opinion of course, be the most helpful, especially to those who are new to binders.
Using the average measurement (i.e underbust plus fullest part of bust, then that answer divided by two) I think would be the most effective, as this is how most websites selling binders measure size. A lot of people, me included, have problems by being between two sizes, therefore, having this as the standard way of expressing chest size on here would, in my opinion of course, be the most helpful, especially to those who are new to binders.