As I also added into discord: If you stick to intervals of 3 minutes and 15 seconds (properly 194.4 seconds) then speed in knots shows itself as a distance in hectometer units (100m) between the plots. As such, 13 minutes is a nice round number period to average the plots over 4 intervals.
If you were to measure in imperial units (yards) then it would require 3 minutes.
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