ok thanks for the reply, the reason i ask is ,while out in my boat yesterday i had to tow a fellow home who had broken down,while doing this i set my unit to record & slowly headed back to his ramp,on the way we passed some artificial reefs that have been put into our lake,now as i got close to some of these reefs i noticed that these reefs were slightly away from the marks that i have inserted,that were provided from our fisheries website here in aus.I zoomed right in & they were still off the mark, would using map offset correct this,bearing in mind i do not have a navionics card ,just the standard base map & having watched the how to map off set video, it explains to use a structure like a bridge to go off, this system does not have anything like that.
thanks T.G