Grand Jour Instruction Manual
Automatic Mechanical Movement — Miyota 8285 Caliber
Crown Positions
Three-position stemThe crown is the small knurled dial at the 3 o'clock side of the case. It clicks into three distinct positions, each with a different function.
Setting the Time
Position 2- 1Pull the crown out to Position 2 — the second hand stops instantly. This is the hacking function, and it's what lets you land on the exact second.
- 2Turn the crown in either direction to move the hour and minute hands to the correct time.
- 3Push the crown back to Position 0 at the moment your reference clock's second hand hits 12, so the seconds hand resumes in sync.
Setting the Date and Day
Position 1 · Quickset- 1Pull the crown out to Position 1 — the first click. You'll feel the stop.
- 2Turn clockwise to advance the date disc forward one day per click.
- 3Turn counterclockwise to advance the day-of-week disc forward one day per click.
- 4Push the crown back in to Position 0 once the correct date and day are both showing.
Between roughly 21:00 and 01:00, the date and day gear train is already engaged in its slow mechanical switch-over. Forcing the quickset during this window can bend or break the jumper mechanism. If you're not sure what time the hands are showing, set the hands to a safe time (e.g. noon) first, correct the date and day, then set the correct time.
Resizing Your Band
Presidential / Jubilee linksThe Presidential and Jubilee bracelets are held together with small screws between each link, not push pins. Every box ships with a small screwdriver for this — removing links shortens the bracelet, and the same links can be put back in to lengthen it again later.
- 1Find the screw on the link you want to remove, on the underside of the bracelet.
- 2Use the included screwdriver to turn the screw counterclockwise. As it loosens, use a small paper clip (or similar thin pin) pressed against the opposite side to push the screw through cleanly as you unscrew it, rather than letting it bind.
- 3Remove links in pairs from both sides of the clasp evenly, rather than all from one side, to keep the clasp centered on your wrist.
- 4Rejoin the shortened bracelet by lining the remaining links back up and threading each screw back in with the screwdriver, again using the paper clip from the back to keep it going in straight.
- 5Check the fit on your wrist before wearing it out. Keep the removed links and screws in case you need to lengthen it again.
The screws are small and easy to lose. Work over a table or tray, and don't overtighten when rejoining — snug is enough. If you're not comfortable doing this yourself, most jewelers and watch shops will resize a bracelet for a small fee in a few minutes.
How It Works
Movement mechanicsA semicircular rotor swings freely on a pivot in the center of the movement, driven by the natural motion of your wrist. As it swings, it winds the mainspring through a reduction gear train. The same mainspring can be wound manually by turning the crown clockwise in Position 0 — useful when the watch has stopped, since a rotor-only wind can take hours of wear to build a full charge.
A fully wound mainspring stores roughly 40 hours of running energy, released at a steady rate through the going train to the balance wheel.
The balance wheel and hairspring oscillate at 21,600 vibrations per hour — 6 beats per second — controlled by the pallet fork and escape wheel. This beat rate is what gives the seconds hand its slightly stuttering, mechanical sweep rather than a smooth quartz glide.
Pulling the crown to Position 2 engages a hack lever that physically touches the balance wheel and stops it dead. This is what allows exact-second time setting — release the crown and the balance resumes oscillating instantly.
A star-shaped date wheel and a separate day-of-week disc are each advanced once per 24 hours by a finger cam on the hour wheel, snapping both over near midnight. The quickset lever at Position 1 lets you push the date wheel clockwise or the day disc counterclockwise manually, independent of one another, without moving the hands.
21 synthetic ruby jewels sit at the movement's highest-friction pivot points — balance staff, pallet fork, escape wheel, and the automatic winding bridge — reducing wear and holding lubrication where it matters most.
Specifications
| Caliber | Miyota 8285 |
| Type | Automatic mechanical, hand-wind & hacking |
| Jewels | 21 |
| Frequency | 21,600 bph (3 Hz / 6 beats per second) |
| Power reserve | Approx. 40 hours, fully wound |
| Accuracy (factory spec) | −20 to +40 seconds/day, position-dependent |
| Functions | Hours, minutes, hacking seconds, date, day of week |
| Manual winding | Clockwise, Position 0 |
| Date quickset | Clockwise, Position 1 |
| Day quickset | Counterclockwise, Position 1 |
| Case diameter | 40 mm |
| Movement diameter | 26.2 mm |
| Movement height | 5.7 mm |
Care
Handling notes- 1If the watch has stopped, give the crown 20–30 manual turns in Position 0 before setting time — this brings the mainspring to a safe running tension before you rely on wrist motion alone.
- 2Keep the watch away from strong magnets (speaker magnets, phone cases, laptop latches). Mechanical movements can be magnetized, which throws off accuracy until demagnetized.
- 3Avoid quicksetting the date or day during the 9 PM – 1 AM changeover window described above.