French?, mid 18^th C, engraved ‘J. B. Python Liet Colonel Invenit, Fresselicque Lx fecit’ in copper plate script to the top surface, constructed of a white silver metal with blued steel screws, with fold up sights to each half of the folding rule, engraved to the rear with a scale engraved ¼ ½ & 3/4 to one side and 1-7 on the other side with alchemical symbols possibly corresponding with astronomical bodies, each arm with a fold out steel tip for measuring the internal dimeter of a gun barrel and the diameter of shot, a fold out scale is used to measure diameters and is engraved in Latin for ‘Bala’ Bullet in English and ‘Boca’ mouth, the scale on the front used in conjunction with the spirit level as an inclinometer, length 22cm