Thanks for the replies but as I said I'm a complete ignoramus when it comes to technology so don't understand what either of those 2 things mean
Recalculate - With a route set-up on the GPS you're riding along and either inadvertently or deliberately deviate onto another road. With automatic recalculation the GPS will make changes to the route to get you back on track usually heading for the nearest point you have defined in plotting the route. These can be at two levels:
1/ Way-points (more dominant) or shaping nodes (less dominant). You set either/both of these up using Mapsource on your PC, generally way-points for places you must visit, say; a meeting point, a lunch stop etc. or even your final destination.
2/ Shaping nodes you use for the purpose of making the route follow the roads that you want to ride and that's their only purpose.
With recalculation turned off the route will not be altered and you can rejoin it as you wish and carry on. As to what happens re. directions when you're off route I don't know as I've never tried it (despite having the option with my SP2720), perfectly happy with auto recalc myself. Maybe someone else would care to enlighten us in this respect
Loading routes from Mapsource - Mapsource is the program that you can use on your PC to plot routes that you define, it employs the same mapping data that's on your GPS. This is opposed to just telling the sat nav where you want to go and letting it decide on the route.
As motorcyclists we tend to favour roads that don't necessarily take the fastest or shortest route to a destination and can frequently be circular in configuration. For recreational bike use a sat nav that doesn't have the facility to follow a specific user defined route is pretty useless.
Loading a route from Mapsource is simply the process of transferring a route that you've created from Mapsource on your PC to your Garmin GPS, usually this is done via USB or can be performed by writing the route to an SD card that you insert into the slot on the sat nav and then import.
Effective route creation and the use of Mapsource does take a little getting used to so don't expect to buy a Garmin three days before a Continental tour and not have a frustrating time. However, with a little experience it will become a liberating tool that make trips over unfamiliar roads a pleasure.
Last year I did a 2500 mile French tour with my best mate and although we did deviate from the intended route marginally, the initial of the route was planned months in advance. We followed lots of minor roads in the Alps and South without having to stop and refer to maps and as a consequence made decent progress. Research using Google Streetview and Michelin maps (with the green lines) found us riding some really great twisties we otherwise would have missed. The changes we made, mainly due to the fact that our spare contingency day allowed us to extend our route in the South, were planned on my Netbook and uploaded to my Garmin at the campsite the evening before.