There is no standard spacing that we are aware of. However, there are some general guidelines. For smaller residential systems, measurements at the four corners of the array may be enough. For larger systems, it may be desirable to take measurements every 20 ft (6m) or so in both directions. Data can be taken in a grid pattern at specific points. When near obstructions, such as a roof mounted air conditioner, it may be desirable to take more readings from the closest point on the array. As a reference point, the state of California CSI program requires that the distance between readings NOT exceed 40 feet (12m). The California New Solar Homes Partnership program requires worst case measurements of obstruction angles, so it requires measuring from the point on the array closest to obstructions, not necessarily in any fixed grid pattern.