A spectrum analyzer seems the answer.
In a very practical way I can describe dowsing a person.
This involves dowsing rods typically made from coat hangers, formed into ninty degrees angles of six inch by thirteen inchs.
held in each hand they will respond to your thoughts, so if you think of the resonant field about anyone they will show this by aligning to that field structure, the consequence is a circuler field that is measurable around a person, the young indigo children have a 55 feet radius, the very elderly and ill people right down to almost zero, trial and practise give a dowser the ability to see this at will and thus determine the output of a person, we need to learn how to re-charge, and how to avoid mobile phones, they seriously deplete your output.
http://en.wikipedia.org/wiki/Spectrum_analyzer
Hobbit