Perpetual Calendar - Discovery Series, Caliber 6M13, 1991
and a really easy to open watch. I was using my fingernail to find the groove that allowed to insert the case opener knife. I was a bit worried when looking with the loupe at the case back. The case back is a bit elevated and that means, you can not simply rest the case opener knife on the lugs to create a nice torque. That is at least my safest way to open watch cases without leaving marks. But this one turned out to be a walk in the park. Once I located the groove at the 9 o'clock position, I simply squeezed my fingernail into it to see whether it would move. And it did, by driving the fingernail around the slot, I was able to open the watch without any tools.
The serious way to open this case back is to locate the groove which is at the 9 o'clock position in the case back if the case back is snapped on with the case back picture aligned nicely (the way these watches were closed in the factory). Then use e.g. this Bergeon opener to slightly lift the case back up. On my watch, the case back does not really sit very tight and thus the watch can be opened without leaving prying marks on the case back.
The single coil tells you, this movement has one step motor. And of course, also the dial will tell you this, since all the functions are offered via the central canon pinion, except the 24 hour subdial. The function setting triangle is controlled by your finger's energy while turning the crown. Why am I mentioning this, because SEIKO normally is not shy to put up to 5 step motors in a movement. The typical Seiko Quartz Chronograph with 3 subdials will feature 4 to 5 step motors. You will easily identify those by the number of the coils visible even if the static protection shield is still mounted.
Battery type is SR927W or Renata 395. And please do not forget to shorten the AC and the Battery plus after exchanging the battery. Actually there is a sticker in the case back reminding you of this. After the battery has been exchanged, set the watch to the 0-Match function, pull out the crown and adjust the hands position by pressing one of the 4 pushers. Quite simple, just keep depressing the buttons until you see which hand will start to move. Move all the hands to the 12:00 position. The golden end of the hands, the black or red half moon ends point to the 6 o'clock position and are used for the calendar display.
Important while resetting: the date has to be set to 1.
No need for a manual really, even this watch has quite a few complicated calendar functions.