Is the string-line historically considered the most accurate means to control longitudinal grade?

The statement that the string-line is historically considered the most accurate means to control longitudinal grade is true. Utilizing a string-line for grade control provides a visual and physical reference that allows operators to maintain consistent elevations and slopes during the paving process.

When using a string-line, it runs parallel to the desired finished surface of the asphalt. As the paving machine moves, the operator can adjust the height and angle of the screed based on the line, ensuring that the asphalt layer is laid evenly and meets specified grades. This method is particularly effective because it allows for real-time adjustments, improving height accuracy compared to methods that rely solely on measuring tools or leveling devices without immediate visual feedback.

In contrast, many other methods, while useful in certain contexts, do not offer the same combination of immediate visibility and adjustability that a string-line provides. This makes the string-line method a historical standard in asphalt paving for achieving precise longitudinal grades.