What should be used to lay out a long, straight line of floor accurately?

Using chalk and a mason's line is an effective method for laying out a long, straight line accurately on the floor. The mason's line provides a taut reference that is essential for achieving precision over extended distances. This technique allows you to pull the line tightly between two points, ensuring that the chalk can be snapped against the surface to create a sharp, clear line on the floor that serves as a guide for further work, such as installing flooring, tiles, or marking boundaries for walls.

The other options may not provide the same level of accuracy or ease for setting long, straight lines. For example, while a tape measure and level are useful for measurements and checking horizontal or vertical alignment, they do not directly aid in creating a straight line across longer distances. String and markers can work, but they might not offer the same tension and precision as a mason's line. Similarly, a pencil and straightedge help in drawing lines but are generally more suitable for shorter measurements and not for longer layout lines like those required on floors.