I’m sure there are other ways to do this but I found my 800 (with OS maps) that the advance notification didn’t always notify in time. A TCX file with an embedded cue sheet works, for me, very well. I used RideWithGPS and it generates a cue sheet with the turnings on ..then on Export is option ‘Notify before turn’ and an option to specify how many metres in advance.
Examining the contents of the .TCX file I can check it has the correct detail…it has ‘CoursePonts’ (instructions in the Notes) at the end of the file like this:-
<CoursePoint>
<Name>2nd exit B</Name>
<Time>2015-03-31T22:32:15Z</Time>
<Position>
<LatitudeDegrees>53.72179885518312</LatitudeDegrees>
<LongitudeDegrees>-1.86387494957743</LongitudeDegrees>
</Position>
<PointType>Straight</PointType>
<Notes>At the roundabout, take the 2nd exit onto Barum Top/A629</Notes>
</CoursePoint>
<CoursePoint>
<Name>Commercial</Name>
<Time>2015-03-31T22:41:45Z</Time>
<Position>
<LatitudeDegrees>53.72097580933216</LatitudeDegrees>
<LongitudeDegrees>-1.8615295233303988</LongitudeDegrees>
</Position>
<PointType>Right</PointType>
<Notes>Turn right onto Commercial St/A629</Notes>
</CoursePoint>
I felt that on a recent group ride that I was generally aware of upcoming turnings before others in group who I presume were relying on the GPS to auto notifications.
oh yeh…before starting chose course, settings , turn guidance on