Correct, eprouvette, used by powder manfacterers,vendors, military, and ammunition loading businesses etc to test the brisance ( strength) of a given black powder. There was ( and still is) a considerable variation in strength of black powder even of the same grade, especially between different manufacturers. The scale was meant just to provide a figure for comparison. If brand A powder is snappier than brand B it will affect your velocity, trajectory and power. This one appears little used. They are a curiosity now and quite scarce, not necessarily valuable as collector interest is low.