Yamaha have been adding serial numbers to their pianos since 1917, they consist of a factory code at the start (or none for Hamamatsu) followed by sequential numbers which are specific to each Yamaha factory.
This tool works by firstly decoding the Yamaha factory code from your Yamaha grand piano or Yamaha upright / vertical piano to see where it was made and then comparing the rest of the serial number with records for the first and last manufactured pianos in each year from that specific Yamaha factory. It covers any Yamaha piano made between 1917 and 2012 in all 6 factories. If you get unexpected results please double check that any letters at the start of the piano's serial number aren't actually the end of the Yamaha model number or relate to characteristics of the piano such as scale or finish. Perhaps try it without the letter and see if that matches up with what you already know about the piano.
Enter your Yamaha piano's serial number. It can normally be found somewhere on the piano's gold plate.
Yamaha Serial number :
Click herefor an idea of what this Yamaha piano may be worth