Seagull Caliber ST-1901B

The Seagull caliber ST-1901B is a bicompax handwound chronograph movement found in the Studio Underdog 01SERIES Gen3 (introduced on November 14, 2024 with pre-orders open on November 19, 2024 for 9 hours only).

In Studio Underd0g’s own words:

@studio.underd0g posted the following announcement on their Instagram page on 11/14/24:

“In April 2024, the manufacturer of the ST-1901, Seagull, published an official notice that outlined some major changes to the future supply of all ST-19 series movements. The most notable adjustment being an MoQ (minimum order quantity) increase to 10,000 pieces. Understandably, there has been speculation as to what this could mean for the future of the 01SERIES.”

Although it sounds ridiculous, Studio Underd0g’s claim that Seagull is inflating their MOQs to 10,000 movements was discussed by others back in August 2024 (watch the video).

The caption continues…

“While many brands are saying goodbye to the ST-19 calibre, we’ve signed an exclusive contract with Seagull, allowing us to offer a bespoke version of this column wheel chronograph movement; the ST-1901B.

Developed in partnership with Seagull, the ST-1901B features an all black main plate which beautifully frames the bridges, wheels and balance. The changes are not just cosmetic as we’ve also added a silver swan neck regulator to allow for more precise regulation. All ST-1901B movements are regulated in Great Britain to -10/+15 seconds per day, a major improvement from the previously offered -15/+35 seconds per day.” –Source

The “B” in ST-1901B:

Studio Underd0g has confirmed that the “B” in the exclusive ST-1901B stands for black. Although, Caliber Corner thinks it should have been ST-1901BS – “BS” as in black and silver (and also the new MOQ requirements which are also BS).

While this isn’t the first time we’ve seen a black ST-1901, the Studio Underd0g version adds a twist by mixing a black mainplate with silver bridges to match the chronograph components.

Editor’s Comment: As of now, the ST-1901B does not have a caliber number or brand logo engraved anywhere on the movement. Given the circumstances with Underd0g’s exclusive deal and industry uncertainty with future ST19 availability, Caliber Corner would like to have seen some type of identifying mark on the movement. However, it’s understandable to forgo this for two reasons: cost and time. Not to mention, the ST-1901B doesn’t exactly have a lot of real estate for such customization, and the brand likely does not want to distract from its beauty – still, there are creative ways to handle branding on a movement, if not simply going the traditional route by marking under the balance wheel.

Swan Neck Regulator:

The brand also opted for a swan neck regulator upgrade:

Column wheel chronograph:

The ST-1901B has design roots based on the historic Venus column wheel chronograph framework.

Accuracy:

As mentioned in the quote above, Studio Underd0g performs the regulation of the ST-1901B in their facilities in Great Britain. Watches ship out timed to -10/+15 seconds per day.

Watches with this movement:

At the time Studio Underd0g introduced the ST-1901B with the black mainplate, it is only found in the Gen3 01SERIES models: Watermel0n, Desert Sky, Go0fy Panda, and Mint Ch0c Chip.

One way to determine if a watch is a Gen3 is by looking at the bottom lines of text on the dial. Gen3 pieces will have “Assembled in Great Britain“, whereas previous models will say “Mechanical Hand Winding”.

Assembled in Great Britain:

“Assembled in Great Britain” refers to the overall watch, including installing the dial and hands, crown and stem, casing the movement, attaching a strap, etc. The movement itself is assembled in China and shipped to Great Britain where Studio Underd0g employs a subcontractor (Horologium) to regulate the movements and perform final quality control/testing once the watches are fully assembled.

“The process includes demagnetization, accuracy / rate review (3 positions) and regulation. A report card is included with every watch.”-Source

Additional Resources:

• Studio Underd0g official site