Course feature on Garmin 910/310

Anyone use the "course" feature on the Garmin 910 or 310? Going on vacation soon and someone gave me a gpx track of a run that looks good, but perhaps a bit hard to follow in spots. I thought I'd give the course feature a try on my Garmin. I've got the course loaded into my watch, but my start point will be at a different location than the original start was. For example, suppose the entire course is a circle. If the original course was recorded starting at the right hand side (0 degrees) and run counter clockwise, but I start at the left hand side (180 degrees) and also run counter clockwise how does the Garmin behave?

Would I have to run all the way back to 0 degrees for the course to start? Will it start at 180 and guide me back to 0 then stop? Etc. Hope this makes sense...