During retensioning, what is determined by using a straightedge or string stretched across the pulley tops?

Using a straightedge or string stretched across the tops of the pulleys during retensioning is a method used to assess alignment. This technique helps to identify any misalignment in the pulleys by visually evaluating the straightedge or string's relationship to the pulley surfaces.

When the string is properly aligned with the tops of the pulleys, it indicates that the pulleys are set up correctly in line with one another. If there are any gaps or deviations along the length of the string, it signifies that adjustments are needed to bring the pulleys into proper alignment.

Deflection refers to the movement or bending of a component under load, tension relates to the force exerted by a tightened belt or cable, and angle typically pertains to the geometric positioning of components. In the context of evaluating pulleys, the primary concern is alignment, which is why this method is effectively used for that purpose.