Aligning from the mid-point

 If intermediate points are to be aligned within a line of measurement and each of the two end points cannot be seen from the other, proceed as follows:

1. Select two points 1 and 2 (both approximately in the alignment) from which both end points A and E are visible. Use sight poles to mark the points. 2. From point 1, align point 2 in the straight line 2 - E  4. From point 3, align point 4 in the straight line 3 - A and continue in the same manner until no further leteral deviations are visible at the two inter- mediate points.