Seiko Caliber Y301

The Pulsar (Seiko) caliber Y301 is a vintage quartz movement with 3 jewels. This movement is made by Seiko for Pulsar branded watches. You may also see this caliber listed as Hattori or S. Epson.

The Pulsar user guide for timepieces powered by the Y301 is titled: “Super Accurate Analogue Watches”

Accuracy Rating:

Official Seiko documents state that the calibre Y301 has a loss/gain or average accuracy rating of +/-10 seconds per year. This accuracy rating positions this caliber in a category that is commonly referred to as a “high-accuracy quartz” movement (aka “HAQ” movement).

Official information from Pulsar regarding the accuracy quote (Pulsar manual, pages 6, 7):

“Annual rate : Approximately 10 seconds (Cal. Y301) / 20 seconds (Cal. Y302) when used on the wrist approximately 12 hours a day.

Monthly rate : ±2 seconds (Cal. Y301) / ±4 seconds (Cal. Y302) depending on the manner in which the watch is used.

Note on annual rate: Annual rate is not an aggregate of monthly loss/gain that accumulates in a year. The amount of loss/gain fluctuates depending on the condition of use as shown in the figure below. Annual rate specifies the range of loss/gain that is never exceeded at any given time of a year.”

Accuracy and Temperatures:

Also from the manual (same pages as above):

“Loss/gain in normal temperatures of between 5°C ~ 35°C (41°F ~ 95°F).

To maintain the accuracy of the watch, it is recommended that it be kept in a temperature range between 5° C and 35° C when it is not worn on the wrist.”

Battery Life:

Owners of watches with the Y103 will be delighted to know that even as a super accurate movement, a fresh battery can get up to 3 years of runtime.

A note on battery life from the Pulsar manual:

“As the battery is inserted at the factory to check the function and performance of the watch, its actual life once in your possession may be less than the specified period.” -Pulsar (page 5)

Cal. Y301 VS Y302:

There is a similar caliber Y302 with three main differences. First, the Y301 being discussed on this page is a time-only movement without a calendar complication, whereas the Y302 has a date. Second, is a different in the accuracy rating between the two movements:

• Y301: +/-10 seconds/year
• Y302: +/-20 seconds/year

While the accuracy difference is not dramatic by any means (+/-20 seconds per year still puts the Y302 in HAQ tier), watch enthusiasts wanting extreme accuracy for bragging rights would likely be happier to own a watch with the super accurate Y301.

Why the disparity you ask? It’s likely due to the calendar system adding a very slight extra amount of drag, resulting in minimal accuracy variations which add up over a year to be slightly up or down compared to the calendar-less (hence no-drag) Y301. Keep in mind that, these ratings are given in the span of “per year”, the per day or per month would barely be noticeable. Also, these are just average quotes offered by the manufacturer and it’s possible that a Y301 and Y302 could perform very similarly when tested side-by-side.

The third difference between these calibers is the measurements. The datewheel on the Y302 extends beyond the actual movement, making it a 23mm overall diameter, compared to 20mm for the Y301. Thickness is also affected, with the Y301 at 1.6mm and the Y302 at 1.9mm tall.

Y301 VS Y301A:

The trailing letter (A) in Y301A is simply an evolution marker or version. There is no difference between Y301 and Y301A, since the A just indicates that it is the first version. There does not appear to be a second (B) or third (C) version. You may see this calibre referred to as Y301, yet when you open the case to see the movement, it will likely be engraved with “Y301A”.

User Manual for watches with Y301:

Additional Resources:

• List of Seiko watch movements