Which type of surveyor's level maintains its line of sight in the horizontal plane automatically?

An automatic level is designed to maintain its line of sight in the horizontal plane without the need for manual adjustment. This is achieved through the use of an internal compensator that balances the instrument, allowing it to self-level on uneven ground. The automatic leveling feature significantly enhances efficiency and accuracy, as it eliminates the potential for human error during the leveling process.

In contrast, a survey level typically requires manual adjustments to achieve a precise horizontal line and does not have the same built-in compensatory mechanism. A digital level, while advanced in readings and data collection, may not necessarily provide the automatic leveling feature inherent to an automatic level. Similarly, a manual level lacks the automatic compensation and requires careful adjustment by the operator to ensure that the line of sight is truly horizontal.

Thus, the automatic leveling capability of the automatic level sets it apart as the most effective choice for maintaining a consistent horizontal sightline in surveying tasks.