Which combination has a maximum average triangle closure of 2 arcseconds?

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

Answer: (D)

Triangle closure error tells us how much a closed triangle in a network deviates from perfect closure due to measurement errors. The amount we’re willing to tolerate depends on two factors: the order of the triangle (how complex or data-rich the element is) and its class (the quality category of the network, with Class I being tighter in accuracy and Class II being looser). Higher order triangles tend to accumulate more small errors because more measurements contribute to the closure, and a lower-quality class (Class II) accepts a larger overall discrepancy. So the largest tolerated closure appears for the combination with the highest order and the least stringent class. That is why the maximum average triangle closure of 2 arcseconds corresponds to the third order, Class II. The other options would have smaller allowed closures due to either lower order or a tighter class, which constrains the closure more.