Yeah, the problem with that UI is it doesn't get updated immediately and it's the total for 7 days. With multiple apps running it is difficult to isolate what is being counted.
I see that REST (I have been using SOAP) has the Get Daily Usage method, so that should work. I can already see that getting stats itself also counts as an API call (!) so it's clear that pagination is irrelevant (that is, every call counts). On the other hand, REST is more generous with batch size (max of 300 results at once, as opposed to SOAP's max of 100) so that will be helpful.