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On many watches, you will find two different serial numbers: one on the case of the watch, and one on the interior mechanism of the watch. This is because the two are often manufactured separately. If you check both the case and the mechanism and discover that they were made in different years, this can be due to several reasons. If the difference is only one year, it may simply be that one component was manufactured first and then warehoused until it was needed to assemble the watch. If the difference is more than a year, it is likely that one of the elements has been replaced. To find the serial number on the case of your Bulova watch, simply flip it over and look at the flat back of the case. If there is a serial number, it should be engraved here.  Serial numbers do not all contain the same number of digits. Not all Bulova watches will have serial numbers on the case. If yours does not, you may want to consider looking for a serial number on the mechanism. You may want to use a magnifying glass to help you read the serial number. If you already looked for a date code on your watch, you may have already found the serial number. If there are no identifying marks on the outside of your watch, or if you want to know the model number of the movement that was used in your watch, you will have to take the back case off. The serial number may be located anywhere on the mechanism. Be very careful doing this, as you can damage the watch if you are careless.  Be sure to place the watch on a soft cloth as you are working in order to prevent it from getting damaged. If the watch has a snap back case, you should be able to see a raised lip around the back and bezel of the case. There won't be any hinges or notches. Snap back cases simply snap into place, so you should be able to remove one by prying it up with a dull tool. Don't use anything sharp (like a knife blade) that you might cut yourself with. Some older watches have swing-back cases, which can be identified by a hinge on the back of the case. These are opened the same way as snap back cases, but the back hinges open instead of coming all the way off. You may even be able to open this type of back with your fingernail. If the watch has a screw back case, you should see six grooves or notches located somewhere along the perimeter of the metal back. You will need to open the back case using these notches. Screw back cases must be unscrewed before you can lift them away. You will need a special tool known as an adjustable case wrench to open one. There may also be a second protective cover inside of your watch. This can usually be pried off with a fingernail, but be careful not to damage the mechanism as you are doing this. If you have any trouble getting the case open, bring the watch to a professional jeweler. If you opened the back of your watch to locate a serial number, be sure to put it back together right away.  For snap back watches, locate the small pin on the inner lip of the case and the small hole around the perimeter of the watch. Line up the pin and the hole, then press and click the case back on using your hands. For screw back cases, place the case over the back of the watch and grab onto the grooves using the case wrench. Rotate the case clockwise until it screws back into place. Once you have identified a serial number on your watch, you can try searching for the number online or using an online chart to help you identify when the watch was made. There is no official Bulova chart to reference, but many people have compiled charts based on their own observations of patterns.  Some serial numbers are easier to identify than others. For example, watches that were produced before 1926 tend to have serial numbers that start with the numbers 1 or 2, but the exact number does not give any further clues as to its production date.  Between 1926 and 1949, the first digit of the serial number was typically used to indicate in which year within a decade the watch was produced. For example, a serial number that starts with 1 could indicate that that watch was produced in 1931 or 1941.

Summary:
Be aware of the two types of serial numbers. Find the serial number on the case. Find the serial number on the interior mechanism. Replace the back case. Compare the serial number to online lists.