Distance

Thank you for your reply. It was 43.56km.

My GPS settings was auto.

I don't know whether or not the result was good. I think it is not so bad but also thought it was better than it. This was my first time I ran in marathon with the Garmin watch.

So I would like to have known in the marathon whether my watch worked well when I saw the distance.

I think it's due to GPS drift. 

"The GPS location accuracy of Garmin outdoor watches is around 3 meters (10 feet), 95% of the time. This means, at any given time, your watch will save your location within 3 meters of your actual location. If your watch is recording a GPS location every second and you do not pause an activity while standing still, your watch can record up to 180 meters (590 ft) in just 1 minute. When in an area with degraded GPS signals, your watch can record even more distance while stopped. The distance recorded while standing still is a representation of GPS Drift."

So the watch records a slightly longer distance than you really move, since the position is randomly drifting around.

Next time you could try enabling multi-band instead of auto. It will use more battery, but you'll get the best possible accuracy.

Thank you very much for your kind reply.

Now I understand. I didn't know the "GPS drift" and read the Garmin faq you told.

I will try enabling multi-band next time.

Thanks again.

I also found the GPS Drift explanation of the Tokyo Marayhon's case in Japanese Garmin  Faq site. I understood very well.

Thanks anyway.