I’m not positive, but from my investigations, this tool is based on
the ability to surmise the highest possible refractive index based to
the relative reflectivity of the material in question. If you really
are interested in making these things, you might do well to talk to Dr.
William Hanneman in Poulsbo, Washington. He holds patents on some of
these devices and currently manufactures them.
I have his number, if you are interested.