Figure 4-10. Principle of Method For Crossing Obstacles
(3) The instruments should be adjusted as accurately as possible. Refer to the sample DA Form
5820 at Figure 4-11, and use the following procedures to ensure accurate readings:
(a) Read and record the near rod once for each set of 25 readings on the distant rod. For each
of the 25 readings, the drum scale is read three times and recorded. First, set the center thread on the top
target (A) and read the scale. Second, center the bubble and read the scale at C. Lastly, set the center
thread on the bottom target (B) and read the scale. These three readings of the drum scale should be
repeated in the above order until at least 25 have been obtained. The observers then change places,
taking their instruments with them but leaving the tripods.
(b) Two days' observations are required. Each day's observations consist of four sets, two
per observer at each station. These sets should be obtained in the following order: Assume that A and B
are the two stations (refer to Figure 4-9, page 4-22). Observer one takes a set of readings at station A,
transports his instrument to station B, takes two sets, and returns to station A to take another set.
Observer 2 carries out a similar program, beginning at station B.