Your Designjet Serial Number explained
Older HP Designjet Serial Numbers are usually composed of 10 letters and digits, for example ESA4800248 which can be broken down as follows:

Country Code is shown in the first two positions. In the example above 'ES' relates to the code for Spain.

Revision/Printer Version is shown in the third position. The letter A signifies the original printer version, the next revision would be the letter B and so on. 

Year of manufacture is shown in the fourth position. The number 4 relates to 1994 in the example above due to the age of the printer and timeframe of manufacture. It can also represent the year 2004.

Month of manufacture is shown in the fifth position. In the example above the number 8 relates to August. Numbers run from 1-9 and then the code switches to letters to avoid having to provide 2 digits for month 10, 11 and 12. October is therefore represented by the letter A, November by B and December by C.

Unique printer number is shown in the remaining five digits, which distinguishes the Designjet printer from others manufactured in the same country in the same month. In the example above this number is 00248.

More current HP Designjet Serial Numbers are also composed of 10 digits, but the breakdown is different. So taking the example CN1CF1M23C, the first two digits are the Country Code, the third digit relates to the Year of Manufacture (in this case 1 = 2001 or 2011) and the fourth digit relates to the Month of Manufacture (C = December) - all other letters and numbers are unique.