Lab 6 - Differential Leveling Assignment (1)

CE 301 – Civil Engineering Systems Lab 6 – Differential Leveling Page 3 of 5 Tips for accurate readings:  Setting up the automatic level halfway between points will reduce errors due to the curvature of the earth as discussed in your reading. Pace between the two points you’re measuring to find a midpoint and set your automatic level there.  Your level rod needs to be perfectly vertical to take a correct reading. Sway your level rod back and forth over the point while your teammates are looking through the automatic level. The lowest value seen on the level rod is the correct reading.  Use a small square of wood to provide a firm, even surface to rest the level rod on at each point.  NEVER move your automatic level before you have taken both a backsight and a foresight at a point. Calculations Perform a page check when you finish your measurements to verify your calculations. Page Check: ? ?𝑀 𝐾??𝑤? + ∑ ?𝑆 − ∑ ?𝑆 = ? ?𝑀 𝐹𝑖?𝑎𝑙 Find your loop misclosure by taking the difference between your final, calculated elevation of the benchmark and the initial, known elevation of the benchmark. 𝐿??? ?????????? = ? ?𝑀 𝐹𝑖?𝑎𝑙 − ? ?𝑀 𝐾??𝑤? = 𝛿 A simple adjustment procedure is used to cancel out the error accumulated during data collection. The total loop misclosure, δ , is divided by the number of times the instrument was set up, n. This correction value is applied to each elevation calculated in increasing proportion. Thus: ???????? ????????? ?? ? = ????????? ?? ? − 1 × 𝛿 ? ???????? ????????? ?? ? = ????????? ?? ? − 2 × 𝛿 ? Since the elevation of B was measured relative to the elevation of A, we assume that error has accumulated through two instrument setups. Thus, the elevation of E requires the most adjustment.