I seem to be posting a lot about different clinical tests that I knew nothing about when I was a student (for example the lunge test). The navicular drop test is also a test I knew very little about when I was a student. This video explains what it is
Like the lunge test it appears the navicular drop test is used a lot by podiatrists outside the USA and by physical therapists worldwide. It is just a measure of of how much the arch collapses when the foot pronates or supinate so it certainly can be seen how useful it is.