Routing on the 500, I suspect the 510 is very similar.
http://velogps.com/garmin-edge-500-turn-turn-directions-courses/
The 510 is similar - but the 510 fails when the trip is longer than 80-120k's.
I suspect it hits the waypoint limit.
@Thuekr started
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Routing on the 500, I suspect the 510 is very similar.
http://velogps.com/garmin-edge-500-turn-turn-directions-courses/