A couple of years ago I rode from Durness to Dover, I plotted the total route into a Satmap GPS, however I also plotted it on a A5 size Phillips Road map, because Sods law will switch in when you want the GPS route most. GPS are ok when they work but batteries fail, sometimes the GPS cannot get a signal. From my experiences with GPS, they seem to take a lunch break during the period from 12AM to 12.30PM Zulu for updating and servicing.