Which combination has a maximum average triangle closure of 1.2 arcseconds?

• A. Second order, Class I
• B. Second order, Class II
• C. Third order, Class I
• D. Third order, Class II

Answer: (A)

Triangle closure here is about how large the residual closing error is when a network or a set of triangles is modeled. A simpler modeling approach (second order) combined with the less constrained processing class (Class I) leaves more distortions unaccounted for, so the average triangle closure tends to be larger. When you move to a higher-order model (third order) or switch to the more constrained or refined class (Class II), the modeling captures more of the distortions, and the average closure shrinks.

Thus the combination that yields the largest typical closure—a maximum of 1.2 arcseconds—is the simpler setup: second order with Class I. The other options involve more complex modeling or stricter processing that reduce the closure values below that level.