What feature distinguishes a fixed GPS base station?

A fixed GPS base station is characterized by its ability to maintain a stable and precise position over time to facilitate high-accuracy measurements. By remaining in a fixed location, it serves as a reference point for surveying, navigation, and other applications that depend on GPS data. This stability is crucial as it allows for the consistent collection of data, which can be used to correct for errors in GPS signal reception and enhance the accuracy of location measurements.

The other options do not describe the fundamental trait of a fixed GPS base station. Operating on batteries or requiring mobility for adjustments would detract from the consistency and reliability needed for a base station's intended functions. Frequent calibration may be necessary for various equipment, but a fixed base station's primary feature is its permanent location, which minimizes the need for recalibration associated with movement.