While in Add Constraints mode
, you can
constrain the slopes at either end of a spline.
Note: You can also dynamically
modify spline slopes in Select 
mode.
To constrain slopes:
Click the Add
Constraints icon
, from
the Sketcher toolbar.
The cursor changes to a black pointer and
cross-hair. 
.
Click on the
spline. Dashed lines representing the slopes at either end will appear.
Note: The direction of the slope depends on how the slope was defined; the slope proceeds in the order in which the spline points were picked.
Click the desired slope and use the Constraint toolbar to add the desired constraints.
Example:
Click the upper slope and then the
diagonal line. Click the normal icon 
in the Constraint toolbar.
The slope is now normal to the diagonal line.
Now click the lower slope, and click the vertical
constraint icon.
Both slopes are now constrained.
