Tutorial Post 13: Cursor Jumping.

Tutorial Post 13: Cursor Jumping.

While you are moving the cursor with arrow keys and 'B','V','F' keys, the set of reachable positions is limited to the three-dimensional grid of points in the model space separated by cursor step distance in each dimension. You can change the cursor step on the Inputs Page ('QI...'): 

(Note that changing the cursor step also updates the view scale, so that the cursor's size and step remain the same to the observer's view.)
In some cases you may want to move a cursor to some hardly reachable position. For example, you have inserted   a regular polygon (as in Tutorial Post 12) and you want to move the cursor one of its vertices. You may move the the cursor close to the desired vertex (endpoint) and then use the option: 'JUMP TO THE NEAREST ENDPOINT' on the Cursor Menu ('QCJ').

Then the cursor should be moved to the nearest endpoint:

(Note that you have also the option: 'JUMP TO THE NEAREST SELECTED ENDPOINT', which could be useful if you can select between closely placed sets of endpoints.)

Other options for  'CURSOR JUMPING' are available as a sub-menu of  Constructive Methods ('QMJ...').

You can move the cursor to the center of visible constructive points. You can use this option together with the command that sets the constructive points 'U' and 'W' on the bounding box of the selected endpoints ('QMB') available on the Constructive Methods Menu:

 When 'U' and 'W' are the only visible constructive points, the key sequence 'QMJ0' moves the cursor to the center of the bounding box of the selected endpoints.

You may also move the cursor to the centroid (arithmetic mean) of the selected endpoints 'QMJC'. However, be aware that there could be many endpoints in some position, where you see only one selection mark.
There is also option to move the cursor to the intersection of the line 'AB' and the plane 'CDE', where 'ABCDE' are visible constructive endpoints (key sequence 'QMJ1'). See how the yellow cursor has been placed on the figure below: