This document discusses sag calculation in overhead transmission lines. It defines sag as the lowest point of sag between two support structures. There are two types of sag - equal supports and unequal supports. Formulas are provided to calculate sag based on span length, conductor weight, tension, height differences, and additional loadings from ice and wind. Maintaining proper sag is important for safety clearances and preventing over-tensioning of conductors that could cause breaks. Advantages include determining safe tension while disadvantages include potential breaks if sag is too small.