To Reuse a Current Datum Point
1. Click Geometry. The Geometry tab opens.
2. Click > 
Orthogonal Construction.
Orthogonal Construction.3. Right-click and choose Horizontal at Last, Vertical at Last, Oblique +45 at Last or Oblique -45 at Last from the shortcut menu.
4. A construction line is created through the currently selected datum point.
5. Repeat these steps to create more construction lines through the same datum point.