What essential feature must a rolling straightedge have for accurate measurement?

A rolling straightedge is a tool used in asphalt paving to assess the smoothness of a completed surface. The essential feature that it must have for accurate measurement is the ability to provide a readout gauge that shows low and high readings. This feature is crucial because it allows the operator to easily identify any deviations in the surface smoothness. By displaying the measurements directly, it gives clear feedback on whether the surface meets the required specifications for quality.

The functionality of the readout gauge is vital for ensuring that any irregularities can be addressed promptly, thus maintaining the overall integrity and performance of the paved surface. Without this capability, it would be challenging to ascertain the quality of the paving, leading to potential issues with ride quality and durability.

Although a digital display, built-in GPS, or lightweight design can enhance usability, they are not essential for the core function of accurately measuring surface smoothness. The primary requirement focuses on the measurement capability, making the readout gauge the key feature.