Sextant - Cast brass, Mahogany - Firma W. Boosman Amsterdam

This sextant was very likely produced between 1890 and 1920, which means the instrument is currently about 105 to 135 years old.
The exact age can be traced from the engraved maker on the arc:
• History of the maker: The W. Boosman firm was founded in 1836 in Amsterdam. Founder Willem Boosman died around 1880, after which the company (located at Warmoesstraat 97) continued to manufacture and certify maritime instruments under the same name for the Dutch merchant navy and the Royal Netherlands Navy.
• Model features: The specific model (a brass 'three-circle' or 'cross-brace' frame) with this typical silver or white-metal graduated arc was extensively used around the turn from the 19th to the 20th century. The few remaining documented Boosman sextants and octants with similar engravings often carry calibration reports or datings between 1900 and 1919.