A footing is set with a bench mark elevation of 100.00 ft and a back sight rod reading of 4.70 ft; if the bottom of the footing is at elevation 94.00 ft, what is the rod reading for the bottom of the footing?

A footing is set with a bench mark elevation of 100.00 ft and a back sight rod reading of 4.70 ft; if the bottom of the footing is at elevation 94.00 ft, what is the rod reading for the bottom of the footing?

• A. 10.70 feet
• B. 6.00 feet
• C. 1.30 feet
• D. .70 feet

Answer: (A)

In surveying, determine the instrument height (HI) by adding the back sight reading to the bench mark elevation. With a bench mark of 100.00 ft and a back sight of 4.70 ft, HI = 100.00 + 4.70 = 104.70 ft. The rod reading (forward sight) for a point with an elevation of 94.00 ft must satisfy Elevation = HI − rod_reading. So rod_reading = HI − Elevation = 104.70 − 94.00 = 10.70 ft. Therefore, the rod reading for the bottom of the footing is 10.70 feet.

In surveying, determine the instrument height (HI) by adding the back sight reading to the bench mark elevation. With a bench mark of 100.00 ft and a back sight of 4.70 ft, HI = 100.00 + 4.70 = 104.70 ft.

The rod reading (forward sight) for a point with an elevation of 94.00 ft must satisfy Elevation = HI − rod_reading. So rod_reading = HI − Elevation = 104.70 − 94.00 = 10.70 ft.

Therefore, the rod reading for the bottom of the footing is 10.70 feet.