How can horizontal distances be estimated when using an optical level?

Using stadia lines is an effective method for estimating horizontal distances when using an optical level because these lines are specifically designed to facilitate this type of measurement. Stadia lines are two additional horizontal markings etched onto the instrument's reticle. When a surveyor sights a target, they can read the distance to that target based on the differences in the readings between the bottom and top stadia lines and the known distance between those lines.

The formula utilized involves multiplying the difference in readings by a known constant, which gives an estimate of the horizontal distance to the target. This technique allows surveyors to quickly gauge distances without needing to physically measure them with a tape measure, making the process more efficient, especially over long distances or rugged terrain.

This method stands out compared to other options. Measuring with a tape requires physical effort and can be cumbersome in certain situations. Calculating angles may be useful in some applications, but it does not directly provide horizontal distances without additional steps. Using a calibration tool may assist in ensuring accuracy but does not directly contribute to the estimation of horizontal distances when surveying.