(a) (1) Begin by completing the information in the page heading.
(b) (2) Record the readings from the backsight (near) rods (keep a running total).
(c) (3) Record the readings from the foresight (distant) rods (keep a running total).
(d) (4) Enter the means of each set of three thread readings on the near rod and the sum of
the means. (The decimals are not usually shown when recording the mean of the three thread readings;
however, they have been inserted here since millimeters and tenths of a millimeter will be used to help
determine the C factor.)
(e) (5) Enter the thread interval on the near rod. This reading is obtained by subtracting the
middle thread reading from the upper thread reading and subtracting the lower thread reading from the
middle thread reading for each backsight.
(f) (6) Enter the sum of the intervals for each backsight and the sum of all backsights.
(g) (7), (8), and (9) Apply the same procedure used to obtain columnar values for the
backsights, using the readings in column (3).
(h) (10) The curvature and refraction correction (Table 4-1) must be taken out and applied to
the distant-rod readings. Use each foresights separately, and determine the curvature and refraction
value. Sum these values and apply this sum to the sum of the mean values in column (7).
Table 4-1. Total Correction for Curvature and Refraction
EN0593
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