To identify a National cash register, locate the serial number and model code embossed on the machine. The serial number indicates the year the register was produced in the factory, and the model code contains information about its style and construction.
Some National cash registers have model numbers, while others have a combination of letters and numbers that reveal additional information about the register's features. For example, as of May 2015, the number 211 indicates that the register's model number is 211. A register with model code 572-EL-9 is a model 572 with an electric motor and nine drawers.
Other letters frequently appear in National cash register model codes. "L" indicates that the register has electric lights, and "F" indicates a large register that stands on the floor. Registers marked "C" are cabinet-style models, and those marked "G" have autographic printers.
National cash registers produced before 1909 have model numbers only. Those produced after 1909 have serial numbers printed above the model information. Serial numbers are linked to the year the register left the factory but are unrelated to the model numbers.
Serial numbers preceded by the letter "S" indicate that the register was sent back to the factory after initial shipping. These serial numbers reveal the month and year the register was shipped out for the final time. They contain no information about the original shipping date.