I will have to look up the book. However, I think that the answer to the original question is;
VLOC - VOR or Localiser information (depending on frequency in Nav box) - the dots represent angular deviations from a point source (the VOR or the LOC).
NAV - GPS derived information is displayed and the dots represent a certain fixed distance parallel to the chosen track.
Basically, keep it one dot right in VLOC and you will get there (just not on the chosen track) but do the same in NAV and you will never get there - you will simply parallel the desired track and pass 1nm or whatever the scale to one side of the waypoint.
The book should give the exact info.
Regards,
DFC