all future requirements with a minimum of field work.
Sufficient
Pacific Southwest Region
Reproduced from the holdings of the National Archives
controls are available to replace destroyed stations and establish
required new stations.
A new station can be located by forming a
strong triangle with any two of the adjusted primary stations.
PRECISE ALIGNMENT
An unusual feature of the survey program was
ment of the 203 series satetions.
This
the alignment require-
included measurement of a
zero line to a linesr tolerance of not to exceed 1:25000 and establishing a 9000 foot line of sight to a tolerance of plus or
minus one quarter inch.
Vertical control for this alignment was
accomplished by establishing a series of bench marks by precise
differential leveling and applying a correction for curvature of
the earth.
Horizontal control stations were eStabdlished by night
operations with precise equipment and procedures developed to
produce the required accuracy.
The alignment of the stations was
accomplished by offset measurements
from these controls
established working point on each station.
to a pre-