Let's take a look at these watches in the M170 series which include from left to right, M170S with a day and date; the M171S also with a day and date function and the M172S with a retrograde date and power reserve.
Each watch also has a flying sea gull shaped frame that houses the flywheel. In watch jargon it mimics the look of a tourbillon movement, but not the functions. Sea-Gull makes tourbillon movements, but not in the M170 price range.
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French-Swiss watchmaker Abraham-Louis Breguet designed the tourbillion to improve accuracy. Advances in the use of jewels and alloys have replaced the function of tourbillons. They are still included in expensive modern watches as a demonstration of great skill, mastery and expertise in watchmaking. The mechanism is usually exposed on the watch's face to show it off.
Differences in the M170S &171S
The release of model 171S made the M170S extinct. You can find a few models in circulation, however, Seagull replicated its primary functions in the next generation. I suggest that you recognize the differences and keep an eye out for sellers asking the same price as its successors. The product should have a significant discounted price.
If you look at the M170S above (to the far left) you will see day and date indicators. The same functions exist in the middle watch. The M171S, however, has a retrograde month and date function.
The term retrograde means to swing back and start again.
The Seagull retrograde indicators use pointer hands, which return to zero at the end of a prescribed days and, or months. For example a retrograde date hand moves up the scale a day at a time, pointing to the current date. When it reaches 31 it will spring back to 1.
The M170S uses a Sea-Gull Automatic ST2502 movement, while the next generation model uses a ST2504.
Differences in the M171S &172S
Seagull equipped the M172S with a retrograde date and power reserve indicator. It lacks the day of the week indicator, which many watch enthusiasts will forego for the power reserve indicator.
Originally called Réserve de Marche, the power reserve indicator shows the amount of remaining stored energy as a function of the tension on the mainspring at any particular moment. It is one of the most coveted functions of watch enthusiasts, myself included.
Like the tourbillon, the power reserve demonstrates great skill, mastery and expertise in watchmaking.
The M172S uses a Sea-Gull Automatic ST2505 movement.
General Comparison
Below is a comparison of the features of each model
M170S |
M171S |
M172S |
| Hours, minutes, second, day, and date | Hours, minutes, second, day, and date | Power reserve indicator |
| No retrograde complications | Retrograde date | Retrograde date |
| Gender: Men's | Gender: Men's | Gender: Men's |
| Movement: Sea-Gull Automatic ST2502 | Movement: Sea-Gull Automatic ST2504 | Movement: Sea-Gull Automatic ST2505 |
| Case: Premium 316L Stainless Steel | Case: Premium 316L Stainless Steel | Case: Premium 316L Stainless Steel |
| Dimension: 40 x 12mm | Dimension: 40 x 12mm | Dimension: 40x 12 mm |
| Crystal: Sapphire | Crystal: Sapphire | Crystal: Sapphire |
| Water Resistence: 5ATM(50M) | Water Resistence: 5ATM(50M) | Water Resistence: 5ATM(50M) |
| Band: Genuine Leather Strap | Band: Genuine Leather Strap | Band: Genuine Leather Strap |
| Feature: Flywheel; date; Retrograde Date + Week Day optional Gold Rotor | Feature: Flywheel; date; Retrograde Date + Week Day optional Gold Rotor | Feature: Flywheel; date; Power Reserve Indicator; optional Gold Rotor |
| Warranty: 1 Year | Warranty: 1 Year | Warranty:1 Year |
Parnis makes a M172S style watch known as the E388. It's a very close copy of the Sea-Gull model.The Parnis model costs approximately $50 to $100 less than its next of kin M172S.
It uses a Seagull ST2505 movement, so it has the retrograde date and power reserve functions.
Parnis puts a 43 mm case around the movement and uses a plain rather than engraved dial. It has the sea gull shaped flywheel.
Parnis puts a heavier 316L marine grade stainless steel case around the movement and uses a Hardlex crystal (front and back) also known as fused mineral glass. Seiko invented the Hardlex crystal which provides the scratch resistance of Sapphire and a clearer image of the watch than Sapphire. Parnis also included a higher quality leather band.
Hopefully, you found this information useful in helping you make an informed purchase decision.