Always sort out your Geometric Constraints before your Dimensional Constraints.  They are more robust and better capture your design intent.

A Sketch is a set of curves which must be Resolved before it can be used to generate a solid. The Intent Manager constantly resolves the sketch as you add curves to it. To be resolved, a Sketch must contain enough dimensional and geometric constraints to fully describe the curves.

Geometric relations are the most robust way to capture Design Intent in a sketch

 The Intent Manager will automatically assign Geometric constraints as you sketch – do not allow constraint to be assigned if they go against your design intent.  As with dimensions, geometric constraints can be selected and deleted

Sometimes selection can be a bit tricky, if you cannot highlight a constraint by hovering your mouse over it then whilst in the correct position either;

– RMB menu > pick from list – this will show all entities under the mouse pointer

– or, toggle through all the entities in that list with a momentary/quick RMB click until the one you want highlights then LMB to select.

As your sketching and the Intent Manager is trying to apply/snap a particular constraint:

RMB to toggle through lock/disable/enable the constraint

use Tab key to toggle active constraint

press and hold Shift to disable snapping to new constraints

 

  Vertical – a line aligned vertically or two points vertically aligned

  Horizontal – a line aligned horizontally or two points horizontally aligned

 

 

  Perpendicular – 2 curves at 90 degrees to each other – this could be line/line, arc/line, arc/arc

 

 

  Tangency – at the point they meet, two entities are travelling in the same direction – line/arc or arc/arc.  Effectively a smooth transition between two entities.

Tangency on Wikipedia – HERE

 

 

  Midpoint – constrains a point to always be half way along a line

  Coincidence – puts two entities in the same place.  Two points, a point on a line, two lines, two arc centre points [concentricity].  Watch closely for two coincidence constraints in the same place, notice the horizontal and vertical white bars around the constraint circle.

 

 

  Symmetry Centreline – using a centreline as a construction line, you can constrain two points, commonly curve/line endpoints to remain equally spaced each side of that centreline.

  Equality – make two entities equal – lines equal length, arcs equal radius.

  Parallelism – make two lines parallel