I don't understand these units of measurement. Football-field GPS was 4 times less accurate than tennis-field GPS? your reference indicates that uncertainty was 45 meters and became 6.5 meters, one order of magnitude improvement.

To continue with mixed standards -- a tennis court measures 23.78 by 10.97 meters (78 by 36 feet, I'm surprised it hasn't been metrified). The Japanese system should be about 3 orders of magnitude more precise than tennis-court-rated GPS.