A level is set up at a point 150 m from A and 100 m from B. The observed staff reading at A and B are 2.525 m and 1.755 m, respectively. The combined correction for curvature and refraction to the staff reading at A and B are 0.0015 m and 0.0007 m. What is the true difference of the level between A and B?
1
2.5325 m
2
2.1257 m
3
1.7543 m
4
0.7692 m