Thomas Mercer Detent Boxed Chronometer. English, fusee detent boxed chronometer with helical spring not retaining power, 4 in. silvered dial, black Roman hour numerals, Arabic 5 minute markers, half moon up-down indicator and 1.5 in. sub seconds dial, signed, Thomas Mercer, Maker to the Admiralty, London & St. Albans; has blued spade and diamond hands. Has good gimbaled brass tub, bezel with glass crystal and all hardware. In good condition, dial is clean, movement is not running fusee chain is disconnected and spring cylinder spins freely; in original mahogany case with brass handles & key and viewing glass in the lid. Box is 6.5 in. high x 7 in. wide x 7 in. deep