  To study vertical sag requirements and factors affecting the stretched wire
alignment method, the vertical sag equation is first derived theoretically.
Subsequently, the influencing factors,such as the hanging weight or tension,
span length, temperature change, elastic deformation, and the Earths rotation,
of the vertical sag are summarized, and their validity is verified through
actual measurements. Finally, the essential factors affecting vertical sag, the
specific strength and length, are discussed. It is believed that the vertical
sag of a stretched wire is proportional to the square of the length and
inversely proportional to the specific strength of the material.
