Aligning a sketch

When sketching is there anyway to align with another point when
placing a line without placing a reference through the point prior to
sketching?

 

IF you start a sketch without references, you get a warning that you can
ignore. But you have to make sure that by the end of the sketch
everything is referenced somehow to the previous features or you cannot
resolve your sketch and move on. While sketching you can add constrains
to accomplish this, for example to pick the constrains-menu and then
align your sketched line to a point.

HTH

Tom