When Grand Seiko was re-introduced in 1988, their first models had quartz movements. Then, in 1998, Grand Seiko introduced the 9S calibre movement. The first two mechanical calibres for Grand Seiko that were introduced in 1998 were their calibre 9S51 and 9S55. The latter might sound familiar to you if you are into Seiko watches, as it was the base calibre for the 8L35(b) movements used in the Marinemaster series for example. These first two Grand Seiko movements were regulated to perform well within chronometer standards and had a power reserve of 50 hours. Since then, the 9S calibre movements have improved by (a.o.) using innovative materials (resulting in an accuracy of -5/+3 seconds a day on average) and offering a power reserve of no less than 72 hours.