When adjusting an A/C "V" drive belt, how can proper tension be determined?

To determine the proper tension of an A/C "V" drive belt, using a ruler is effective because it allows for a visual measurement and assessment of the belt's deflection. When a specific amount of force is applied to the belt, the distance it deflects from its resting position can be measured with a ruler.

Manufacturers typically provide specifications on the appropriate deflection distance for the belt under a given load. By checking this distance with a ruler, you can ensure that the tension is set to the correct level, which is crucial for optimal performance and longevity of the drive belt and the A/C system.

The other options might not be suitable for this application; for instance, a protractor is used for measuring angles, a scale measures weight, and a vernier caliper is more suited for precise measuring of dimensions. None of these tools can effectively determine the specific tension of a belt the way a ruler can when measuring deflection under the specified load.