The following consecutive readings were taken with a dumpy level and a 3 m staff on a continuous sloping ground:
0.425, 1.035, 1.950, 2.360, 2.950, 0.750, 1.565, 2.455.
Which of the following readings are back sights?
1
0.425, 2.950, 0.750
2
0.425, 2.360, 0.750
3
0.425, 0.750
4
0.425, 2.950, 0.750, 1.565