TlomasLjung, not quite correct these statements below:
but the V/B and V/S will both increase until the V/B is at about 3 to 4 degrees
If VNAV is engaged the aircraft will descend with a FPA equal to the V/B
VB shows you the direct line of sight constant angle from the aircraft the the next point in space (Waypoint) which has a defined altitude (at, ignoring the above or below).
So, be careful with
VB (Vertical Bearing):
When the next waypoint is coded as an A (above) or B (below)
VB does not recognise the use of them thus does NOT use crossing altitude/level but coded altitude/level only.
VB for CDA is great as it gives e.g. constant angle to FAF or other point used in procedure;
But when using it on an approach with minimum or maximum restraints, it does not reflect the path to be flown.
Use it wisely, and it becomes VERY USEFUL;
Ignore its limitations and be in for a surprise one day being high on approach or flying a level segment instead of a CDA.
VB is a calculation of distance versus height only!
VS as on the DESC Page indicates CONSTANT V/S required to achieve
VB