Official dates in Japan are often given by reference to the number of years the then current Japanese emperor has or had reigned. The current era (as of April 2019) is Heisei, which began in 1988 – it will transition to the Reiwa on 1st May 2019. Patent numbers in Japan used to reset with the Regnal year, so between 1989 when patent numbers started with a Regnal year prefix from 1-11, so patent in say 1999 were given a prefix 10, He10 or H10, followed by a hyphen. However, the Japanese patent office ended that practice in 2000, and from then the patent format has been JP20YY-xxxxxx with the year matching calendar years. The previous era too the Heisei was that of the Emperor Showa (known in the west as Hirohito) which ran from 1926-1988, usually designated by an S or Sho followed by the Regnal year.