Hello,
I have been a long time student of USNO marked items, mostly Chelsea clocks, but have studied, chronometers, deck watches, telescopes, binoculars and sextants. All of these type items were calibrated and marked by the Navy. The engravings consist of a stylized N inside an O for Naval Observatory and the item number. The numbers I'm sure had some system but in over 20 years of looking at them I have observed that they are very random. It seems that the numbers were assigned to different items only in the order they were calibrated by the Naval Observatory. I have long searched for the log book recording these items. I have suspected that two Navy shops, the optical shop and chronometer shop had logs and recorded these numbers. I have contacted the Naval Observatory, National Archives, U. S. Naval Historical Center, and Norfolk Naval Shipyard, Portsmouth, Va. all with scant return. The Naval Observatory did the calibration on optical and timekeepers until about 1953 when this task was transfered to Norfolk Naval Shipyard. I have spoken with long time employees of the Norfolk Naval Shipyard and much to my dismay when these shops were closed in the late 1980s the material and records were not recognized as the historical treasure they were. I have found that some chronometer record data from pre 1900 exists at the National Archives but the post 1900 data on chronometers, deck watches, and optical instruments is not to be found. As many have found the Navy overhaul system was only interested in calibrating and returning a working item to the fleet. Boxes and istruments which originally had matching serial numbers were often, if not most of the time, switched during overhaul as the Navy had no interest in the historical significance of matching serial numbers. I have found that production dates of the instruments and the Naval Observatory calibration numbers do not exactly track in line but generally trend in order. Good luck in finding the log books, I have tried for 20 years and the trail grows cold at the Norfolk Naval Shipyard. I hope this information gives some new researcher with time and energy at least a starting point and saves some search time. If I can be of any further help please let me know.
Jim Dyson
Portsmouth, Va.
757-646-1827
www.chelseaclockmuseum.com