Serial numbers associated with pocket watches manufactured by the Keystone Watch Case Co. can be located on the movement of the watch and will help to identify its date of production. It is important to note that there is a second serial number located on the watch case that is unrelated to the one inscribed on the movement, and it should not be used to determine the manufacturing date of the pocket watch.
Charts to match a serial number with a pocket watch's date of production can be found online from watch retailers and repair services like Vintage Time Pieces and Renaissance Watch Repair. The Keystone Watch Case Co. was formerly known as the E. Howard Watch Co.; watch owners who suspect production dates from 1858 to 1902 should refer to a serial number chart specifically for the E. Howard Watch Co., and owners who assume production was between 1902 and 1930 can reference either a Keystone Watch Case Co. or a Keystone-Howard serial number chart.
Additionally, owners interested in information regarding the pocket watch case can determine the quality and rough date of production by identifying the grade of the case. The cases were produced using a range of metals, from nickel to 18K solid gold, and were marked with a grade such as the J. Boss inscription: pocket watches with this marking were known for their balance and guarantee for either 15, 20 or 25 years, as stated by the National Association of Watch and Clock Collectors.