What should the difference between grid azimuths of common control lines, adjusted for angle convergence, be less than?

The maximum allowable difference between the grid azimuths of common control lines, after adjustment for angle convergence, should indeed be less than two minutes of arc. This requirement is rooted in the standards for accuracy in geodetic surveying. Specifically, it ensures that the angular measurements remain consistent and reliable when transformed between different coordinate systems, particularly when converting between grid coordinates and true directions.

The rationale behind the two-minute threshold is to minimize errors that could propagate through geodetic calculations, affecting the overall integrity of the survey results. If the angular difference were allowed to exceed this limit, it could lead to significant miscalculations in positioning, especially when further combining control lines or when applying transformations to real-world locations.

Maintaining such precision is critical in geodetic engineering, as it ensures that the final produced data aligns accurately with the established geodetic frameworks and supports the intended applications, such as mapping, construction, and infrastructure development. Values higher than two minutes can introduce questionable reliability and potential discrepancies in geospatial data interpretation.