"The letters [at the top] are abbreviations for the names of colors in French, found on this page. As for what it is, though, I have no idea. Maybe some kind of divination or pseudoscience tool?"

"I think you are very right; it looks like a variant of an adjustable pendulum. There is a lot of love for pendulums in Southern France, where for centuries, the two most precious things were looked for with twigs, pendulums, and pigs: truffles and water springs. A huge variety of theories and esoteric stuff has been written about that over the years. The truffle site you found is a wonder of such scientific-sounding esoteric stuff.