2. Natural

a. Climate

(1) Description

Weather can have various detrimental effects on angle measurement:

• Heat waves are atmospheric anomalies that can randomly bend the Line of Sight (LOS) displacing the sight or making target pointing difficult.
• Wind may cause the LOS to bounce or make a hand-held target difficult to hod steady.
• A large temperature difference between equipment storage and use requires acclimation time or tripod leg locks may loosen and slip or TSI locks/slow-motions jam.
• Cold uncomfortable temperatures can result in haphazard work.

(2) Behavior

Combined effect is random.

(3) Compensation

In as much as possible select times and locations minimizing climate impacts. Allow equipment temperature acclimation. Dress for conditions.

b. Curvature and Refraction

(1) Description

Curvature and refraction each displace the LOS vertically, though in opposite directions. They affect vertical/zenith angle measurement but not  horizontal.

(2) Behavior

Curvature and refraction are treated as systematic errors.

(3) Compensation

Curvature and refraction are a function of distance and can be mathematically compensated manually or automatically by the instrument.

Curvature and refraction are described in Topic II Chapter E. Systematic Errors