This Ventometer, engraved with the maker's mark "W. Gregory & Co, London," is a precision tool designed for measuring windage or airflow in large bore applications. The instrument features a fine scale and adjustable threading mechanism for precise readings. Its compact and robust design suggests military and field use in ballistic or environmental contexts. The tool remains in good condition, with visible engravings and functional components. Maker's Mark: The engravings indicate "W. Gregory & Co, London," a respected British maker of precision instruments during this era. For Martini Henri and Enfield rifles