Scoob,
I think Kolibear quite clearly knows how to tell his gps to go to C.
He's obviously already told it to go to B, and afterwards to go to C. He's simply interested to learn how the gps decides that he has already been to point B, even though he hasn't actually passed over that exact spot.
Telling it to go "directly to" isn't isn't always such a good option. Especially if you have a flight plan loaded into the gps to go to D, E & F after point C. Using the direct to C in this case, will result in that flight plan being disregarded, and therefore once he gets, to C, he will have to fiddle with it again to direct it to D, and again at E and so on. It's much better that he has done his flight plan on the ground, and don't have to bother with button pushing in the air.
Kolibear,
It's a question I've wondered about too. All I can say, is that it hasn't got it wrong so far, and always seems to know when I've decided to move onto the next point.
dp