In leveling, the first observation is to a known point and is termed a backsight. Which of the following is the correct designation for the first observation?

In leveling, the first observation is to a known point and is termed a backsight. Which of the following is the correct designation for the first observation?

• A. Foresight
• B. Intermediate sight
• C. Backsight
• D. Reversed sight

Answer: (C)

In leveling, you start by establishing the instrument height using a known point. The reading taken on the staff at that known point is called a backsight because you’re looking back toward the benchmark from the instrument’s position. This backsight, combined with the known elevation of the point, defines the height of the instrument (HI) through the relation HI = elevation of the known point + backsight reading. Once the HI is set, you move the staff to the next point and take a foresight, which is the reading on a point whose elevation you want to determine; then you compute that point’s elevation as Elevation = HI − foresight. A reversed sight is when you read the staff in the opposite direction as a check, but it isn’t the first observation. Intermediate sights are readings taken en route between known and unknown points to help maintain accuracy. The first observation is correctly designated as a backsight.