By the late 1700s clocks were theoretically accurate enough to use for navigation (mainly in calculation of longitude)­ but could not remain so if subjected to constant pitching and rolling at sea. To keep their mechanical movements steady they were housed in weighted brass cases mounted in gimbals inside lidded wooden cases, and this remained necessary for seafaring chronometers until well into the 20th century. The originals are now highly collectible. Our beautifully finished replica looks the part but actually has a quartz movement that is more accurate than they could dream of 200 years ago! Case measures 7" square, height 6".Uses one AA battery.