Tip o’ the pileus to Laval Hunsucker on the Classics list for this one … a potentially useful bit of technology for reading/photographing inscriptions (although I would have liked to see what it did with the wooden example at the beginning):
RTI has been around for a while (there are actual tutorials at Youtube on how to do it), we should note … what seems to be new here is the device …
rogueclassicism 
I was also puzzled by the apparent lack of result with the wooden tablet. But I think what I had been expecting was some spectacular result like the recent one with the Archimedes palimpsest, which had been clarified by a much more complex method involving different wavelengths of light, and much image processing. This device, clever as it is, doesn’t do more than shift the source of illumination, and on a piece of wood where the scratched lettering is obscured by the grain it can’t do all that much. However, in real life rather than in a demonstration video, the observer would be able to clarify the outlines of the fainter letters by rotating the source appropriately to bring out scratched lines at different angles.