As I understand it, scalar as of yet can’t really be measured. How do you know that the frequency that you have chosen for a treatment is being transmitted by the scalar?

It is true that it can not be measured directly. But you can see that a full circuit has formed through the light of the tester coil, or the led from the receiving box. Also you can measure the scalar indirectly by how you field, or by using a GDV camera.