For accurate records, how many different permanent reference objects are needed to measure each valve's location?

To accurately measure and document each valve's location, it is essential to establish a system of permanent reference objects. The use of three different permanent reference objects allows for precise triangulation of the valve’s position. This method ensures that the location can be accurately reproduced and referenced in future maintenance or operational activities.

Having three reference points provides enough data to create a reliable coordinate system. This is crucial in water distribution systems, where the accuracy of such measurements can significantly impact the effectiveness of repairs, upgrades, and the overall management of the water distribution network. Moreover, the three reference points help to eliminate potential errors that could arise from using only one or two points, which may not provide a correct or reliable reference in all cases.

The other options fall short because having only one or two reference objects can lead to ambiguity in location, as these would not adequately define the spatial relationship needed for accurate mapping. Therefore, utilizing three permanent reference objects is the best practice for ensuring precise and dependable valve location records.