a. Complete the heading, as shown.
b. In the object observed column, identify the name of the station and the type of target observed
(such as light or heliotrope).
c. Record the time the observations began in the time column.
d. Record the readings of the circle right (reverse) and circle left (direct). Read the vertical circle,
record the degrees and minutes in the circle column, and make and record the two coincidence readings
of the micrometer drum under the columns headed first and second. Add the two coincidence readings,
and record the average in the mean column. Compute the value of the zenith distance by adding 90, to
the total circle right value and subtracting the total circle left value. The result should be noted in the
zenith distance column. This constitutes one position. At least three positions within a range of 10
seconds are required. The instrument should be reversed between circle left pointing and circle right
pointing for each position. The recorder should remind the observer to level the vertical circle bubble
before each pointing.
e. Record the heights of the stand and the instrument in the remarks column. If the heights of the
lights or other equipment change during the occupation of the station, they should be noted and dated.
Note any other pertinent data.
f. Check all computations and measured distances, and initial each page.
4-14. Abstract of Zenith Distances. An example of an abstract of zenith distances is based on the
quadrilateral shown in Figure 4-15. A sample DA Form 1943 is shown at Figure 4-16. The necessary
data for the abstract are transcribed from the record books, with the exception of steps (6), (7), and (10),
which are computed. The circled numbers in Figure 4-16 correspond to the following steps:
Figure 4-15. Quadrilateral