Node Snap
()
Keyboard: NODE
IntermediateToggles the Node Snap on or off. After you turn it on, the pointer changes to a square at the center of the crosshairs. Any points or vertices you specify are snapped to the point nearest the center of the crosshairs (within the square).
Snap to a point entity.
Use Measure to place points on an entity, and then use Node Snap to draw lines by snapping from point to point along the measured entity. Remove the measure points on the first entity by using the Delete command and choosing Previous Selection from the prompt box.