Spring Drive (SBGA413) - Long Term Accuracy

[gozoner]

After getting my Grand Seiko SBGA413, in large part because of the spring drive technology, I decided to measure the long term accuracy over a full year. I'm 20 weeks in and thought I'd describe the results so far. (During this 20 week period I found myself in Scotland for 10 days; refused to change the time to the local time zone.)

I'm impressed with the accuracy; but, after searching posts on this site, I've found others reporting 0 or 1 second after 3 months?!

Date (weeks)	  Error (sec)    Rate (sec/week)	Rate (sec/day)
06/13/2023 ( 0)	     0		
07/18/2023 ( 5)	    +5                1.0                  0.14
08/22/2023 (10)     +7.5              0.75                 0.107
09/26/2023 (15)     +11.5             0.77                 0.11
10/31/2023 (20)     +15.1             0.755                0.108

It gets easier to measure the error as it grows; but I've started using a G-Shock chronometer with >1/10 second resolution recently - which probably explains the first error of +5 being larger and second error increase of 2.5 being smaller.

Total error is +15 seconds over about 4 1/2 months which is well below the stated accuracy of 15 seconds per month. Should I be disappointed?

I'm keen to keep the test going for a full year - which will mean handling daylight savings time by presetting the error when changing the time. We'll see how the watch handles the frigid winters.

Cheers.