Which combination has a maximum average triangle closure of 3 arcseconds?

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

Answer: (C)

Understanding how network order and class set the tolerance for triangle closure in triangulation helps explain why the best choice is the combination with the highest precision and the strictest class. The average triangle closure is the mean residual around closed triangles caused by measurement errors. Higher order networks are designed for higher precision, and within each order, Class I denotes tighter quality than Class II. Consequently, the allowable closure error shrinks as you move to higher order and to Class I. A maximum average closure of 3 arcseconds reflects the smallest, most stringent tolerance among the options, which aligns with third order, Class I. The other options either reduce the order or use the looser Class II, yielding larger permissible closures than 3 arcseconds.