(1) In order to avoid instrumental errors caused from using the same portion of the horizontal
circle and the micrometer to make all of the readings for the 16 positions, the readings are
proportionately distributed. This is accomplished by changing the initial setting of the circle and the
micrometer on the first object or station observed in each position. The reason for this procedure is to
avoid the possibility of obtaining all readings from one portion of the circle or the micrometer, which
could result in erroneous graduations.
(2) Circle and micrometer settings are shown in Table 3-1. For the circle settings at each
position, add 11, to the final degree reading of the previous position, with the exception of the 5th, 9th,
and 13th positions. In these positions, add 12, to the final degree reading of the previous position. The
micrometer settings must be made within 5 seconds of those shown in Table 3-1.
Table 3-1. Circle Settings for First-Order and Second-Order, Class I Work
With the Wild T-3
(3) When observing a position, place the vertical hair on the first observed object, with the
telescope in the required position (D is direct, with the circle telescope on the left; reverse, R is on the
right). Using the micrometer screw, obtain the required seconds setting on the micrometer drum. Refer
to the circle and micrometer seconds in Table 3-1. Using the circle setting knob, set the required degree
setting on the circle. Make the final coincidences with the micrometer screw, ensuring that the two
micrometer readings are within 0.3 of a second before dictating them to the recorder.
(a) Continue this procedure on all objects to the right, with the telescope remaining in the
same position, reading the circle and the micrometer (do not touch the circle setting knob). After the
reading has been made on the last object to the right, rotate the instrument and the telescope so that the
telescope is on the opposite side of the object. Mark the reading here in the prescribed manner. The
reading should be about 180 different from the previous reading. Go through the reading
EN0593
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