On an equal arm scale, shift tests should be conducted on:

The correct response is that shift tests should be conducted on each pan at half capacity. This method is used to ensure that the scale remains balanced and accurate when loaded. Conducting shift tests at half capacity allows for the detection of any potential errors that may occur as weights are applied.

When testing at this level, the scale's performance can be assessed under a condition that closely mirrors actual use without overloading the scale. Operating at half capacity provides sufficient load to ensure that any issues with the load-bearing capability or balance of the scale are revealed while still maintaining a safe margin that prevents damage to the equipment. This balanced approach helps ensure the scale's reliability and precision in everyday operations.