This simple but effective way of testing the structural stability of your foot; as postural stability is heavily determined by the structural stability. Follow the steps below:
1) Get in the position as shown.
2) Close your eyes and try to stand still for a minimum of 15 seconds without;
a) Moving the weight-bearing foot.
b) Catching yourself with the other foot.
c) Opening your eyes.
3) Repeat on your opposite leg.
Functional: You stood for 15 seconds without 2a-c happening.
Dysfunctional: One or more of the actions described in 2a-c happened.