Seagull 816.423 Automatic Watch — ST21 Moon Phase, Power Reserve, Pointer Date, 40.5mm

Seagull 816.423 Automatic Watch — ST21 Moon Phase, Power Reserve, Pointer Date, 40.5mm

The Seagull 816.423 is a 40.5mm in-house ST21 automatic watch with three simultaneous complications on a single silver sunburst dial: a moon phase display, a power reserve indicator and a pointer date calendar. Blue hands, synthetic sapphire crystal, screw-down crown, exhibition caseback, precision stainless steel case at 13mm and steel bracelet with folding clasp, 50m water resistance. Available in silver and rose gold configurations.

Key Specifications

Variants

816.423 Silver: Silver-white sunburst dial with blue hands. 816.423 Rose Gold: Rose gold tone case and bracelet — same ST21 movement and complications in a warmer-coloured configuration.

Three Simultaneous Complications

The 816.423’s ST21 movement drives three complications simultaneously on the dial, creating a genuinely multi-layered information display:

Moon phase (upper right): Shows the current phase of the lunar cycle — new moon, waxing crescent, first quarter, waxing gibbous, full moon and the waning phases. The moon phase disc advances incrementally as the days pass. Manual correction is required approximately every 2.5 years as the mechanical 29.5-day approximation accumulates a one-day offset over time — standard for all mechanical moon phase complications.

Power reserve indicator (upper left): Shows the remaining energy in the mainspring. As the automatic rotor winds the spring through wrist motion, the indicator moves toward “full”; as the watch runs without sufficient wrist movement, it moves toward “empty.” This is a practical complication specific to automatics used in watch rotation — you can see at a glance whether the watch needs additional winding or time on a watch winder.

Pointer date (centre/perimeter): A central hand sweeps around the dial perimeter indicating the current date (1–31). The pointer date is a traditional watchmaking complication — more visually elegant than a date window and associated with vintage European dress watch design.

The three complications are balanced across the dial — power reserve upper-left, moon phase upper-right, pointer date sweeping the perimeter — creating a symmetrical layout without visual crowding.

Seagull ST21 In-House

The ST21 is a Seagull in-house automatic caliber with hacking (stop-second) and manual winding. Seagull designs and manufactures the ST21 at its Tianjin facility. The specific jewel count, beat frequency and power reserve duration are not confirmed in available documentation — confirm from the watch or Seagull’s spec sheet on receipt. The exhibition caseback presents the ST21 rotor and movement in operation.

816.423 in the Seagull Range at Jewelry Addicts

The 816.423 is the most complicated automatic in the Seagull branded range at Jewelry Addicts — three simultaneous complications on a single in-house caliber. Compared to the other Seagull models:

The 816.423 is the only Seagull watch at Jewelry Addicts with a moon phase complication.

Moon Phase + Power Reserve at This Price

Mechanical watches with both moon phase and power reserve indicator at 40.5mm with an in-house movement at under $500 are rare. The AGELOCER Astronomer offers moon phase with an 80-hour in-house reserve at $459; the Seagull 816.423 adds the power reserve indicator and pointer date alongside the moon phase on the ST21. For buyers who specifically want all three of these complications on a single watch at this price, the 816.423 is the most complete option in the range.

Who Is the Seagull 816.423 For?

The 816.423 is built for:

• Three-complication buyers who want moon phase + power reserve indicator + pointer date simultaneously on an in-house automatic steel bracelet watch
• Power reserve indicator buyers who specifically want to monitor winding status on a dress watch used in rotation
• Seagull brand buyers who want the most mechanically complex in-house caliber in the Seagull range at Jewelry Addicts
• Rose gold tone buyers who want the warmer case finish on a moon phase automatic

How It Compares

vs. AGELOCER Astronomer Moonphase — The AGELOCER uses Cal.A4610 in-house at 40mm with 80-hour reserve and 3D sculpted moon on leather strap. The Seagull 816.423 uses ST21 at 40.5mm with moon phase + power reserve indicator + pointer date on steel bracelet. Choose AGELOCER for the 80-hour reserve and 3D moon aesthetics; choose Seagull for the three-simultaneous-complication layout and steel bracelet.

vs. Seagull Natural Series Polaris — Polaris is ST17 at 40mm/10mm, time + small seconds only. The 816.423 is ST21 at 40.5mm/13mm with three complications. Both in-house Seagull steel bracelet automatics — choose Polaris for slim 10mm profile; choose 816.423 for the complication depth.

vs. OUPINKE 3189 Plamont Moonphase — OUPINKE has full calendar with moonphase on Plamont automatic. The Seagull 816.423 has moon phase + power reserve + pointer date on ST21 in-house. Different complication sets and movement provenance.

More from Jewelry Addicts

• Seagull Watches at Jewelry Addicts — full Seagull range
• AGELOCER Astronomer Moonphase — moon phase alternative with 80-hour in-house reserve
• Seagull Natural Series Polaris — ST17 slim in-house alternative
• Best Moonphase Watches Under $500 — full moon phase buying guide
• Best Automatic Watches Under $500 — full roundup