No.3. The exact same procedure as no.2 above was carried out, but this time moving the dumpy level 4m from the right pole, sighting the zero mark, rotating the level 180° and sighting the position on the left pole 996m away. The result was nearly the same as the other pole with a deviation of over 14cm higher than the zero mark.
Source:
http://www.rolf-keppler.de/lichtkrumm.htm 