What is an advantage of an Invar leveling rod?

The advantage of an Invar leveling rod primarily lies in its low coefficient of thermal expansion. Invar is a special iron-nickel alloy that exhibits minimal changes in length with varying temperatures. This property is particularly significant in surveying, where precision is crucial. When survey measurements are taken, even slight variations in rod length due to thermal changes can lead to inaccuracies in leveling and other measurements. Utilizing an Invar leveling rod helps maintain greater accuracy by ensuring that the measurements remain consistent regardless of temperature fluctuations, allowing for reliable and precise leveling over extended periods and varying environmental conditions.

In contrast to the other options, while visibility and detachment features may provide practical benefits, they do not directly relate to the fundamental characteristic that ensures the precision necessary in surveying work.