The serial number, embossed on the back of the calculator or printer on a sticker, tells when and where the calculator was build. Calculators build before 1996 have an unique serial number scheme that consists out of 4 digits, 1 letter and again 5 digits.
YYWWCsssss
The first two digits tells us the year of production. This year of production can be calculated by adding 1960 to the first two digits. The third and fourth number tells us the production week.
The letter C gives the country of manufacturing: A = USA, B = Brazil, G = Germany, J = Japan, S = Singapore, M = Malaysia or Indonesia and Q = United Kingdom. The trailing five digits represent an unique serial.
Example:
The serial number of my personal HP-32SII calculator is 3449S86101. This means: Build in 1994 (1960+34), week 49 in Singapore with the unique serial 86101.
After 1996 a second serial number coding scheme was used. The scheme exists out of 2 letters followed by 8 numbers.
CCYWWsssss
The first two letters are used to represent the code of the manufacturing country.
US = USA, SG = Singapore, CN = China, ID = Indonesia and MY = Malaysia.
The first digit is the last digit of the year of production. The next two digits give the production week, the other 5 digits represent an unique serial number.
Example:
The serial number of mine HP-10B is ID02701925. This means: Fabricated in Indonesia, in the year 2000, week 27 with unique serial 01925.
Some Spice series calculator have an asterisk in front of the serial number. This asterisk is related to the keyboard redesigned after the failures in the first series (heavy calculator). See picture below of mine HP-33C.