The true angle can be calculated by determining positions of station points and remaining points. From figure, at position S1, true angle is given as
? = ? + ?₁ ? ?₂.

Due to presence of less order than remaining classifications, tertiary triangulation involves formation of more number of triangles which makes it a tedious process.

Correction of sag can be given as,
C_s = l*W² / (24*n²*p²). On substitution, we get
C_s = 100*1 / (24*6²*9²)
C_s = 0.00142.

The height of instrument and signal in process of Reconnaissance depends upon profile of ground, distance between stations, and relative elevations of stations.

The height of station can be determined by,
h = D²*(1-2m) / 2*R. here, m= 0.07, radius of earth = 6370km. On substitution, we get
h = 44²*(1-2*0.07) / 2*6370
h = 121.54m.

A heliotrope is an instrument, which is used as a sun signal. It consists of a plane mirror to reflect sun?s rays. The line of sight can be telescopic with an aperture consisting cross hairs.

The elevation of a station can be determined by \(h = \frac{D^2 (1-2m)}{2R}\) and from taking its reference h2 will be calculated. It requires certain parameters like keeping line of sight at a height of 2-3 m above point of tangency.

The corrected angle can be determined by using formula,
Corrected angle = ? + ?₁ ? ?₂. On substitution, we get
Corrected angle = 50?46? + 12?24? ? 13?36?
Corrected angle = 49?34?.

The measured base line can contain some errors which will decrease accuracy of output. While using steel and brass wires this possibility increases. So in order decrease prone of having less accuracy, corrections are applied without considering certain parameters.

The classification of survey field into a triangulation system helps in covering entire area, but main intention is to have accuracy in measurement values obtained.