When measuring distances in areas with physical obstructions, such as a lake in a field, surveyors must employ techniques to calculate accurate lengths without direct line measurements. One effective method is the offset technique, which allows for precise distance estimation over inaccessible stretches.

In this scenario, a surveyor must measure a side of an area that crosses a lake. Since the measuring tape cannot span the lake, the surveyor begins by establishing a baseline that aligns with the side across the lake, using a telescope to ensure alignment from one end of the side to the other. This telescope alignment creates a clear, imaginary line over the obstruction, enabling accurate reference points for further measurement.

Next, the surveyor takes perpendicular offset measurements from each end of the aligned baseline to points on the lake's edge, using a compass to ensure the measurements are taken at right angles. By marking these offset points on both sides of the lake, the surveyor establishes a parallel line that is easier to measure. The surveyor then measures the distance between these offset endpoints.

The total length of the side across the lake is determined by adding the measurable distances leading up to the lake, the span between the offsets, and any additional distance on the opposite side. This cumulative measurement accurately reflects the true distance across the lake despite the obstruction.