Title 110 Differential Levelling.pdf ✅

MSTC 109: Leveling 1. Dumpy Level A dumpy level is an instrument used to make elevation readings. It consists of a telescope that can only be rotated in the horizontal plane. Since it cannot be rotated vertically, the telescope must be perfectly horizontal to ensure accurate measurements. A bubble level is used to determine levelness. If the bubble is inside the designated circle, then the instrument is level. 2. Differential Leveling A benchmark is a location whose elevation is already known. It can also be locations that can be reused for future readings, so its elevation is worth marking. Benchmarks are often not near each other which makes reading the telescope difficult. Thus, turning points are used as intermediate locations for easier reading. The reading to a previous benchmark or turning point is called the backsight. Foresight is the reading to the succeeding benchmark or turning point. HIprev = Elevprev + BSprev Elevnext TP or BM = HIprev − FSnext Readings of foresight, backsight, elevations, as well as the elevation of the instrument, are listed in the leveling notes of the surveyor. Station Backsight (BS) Instrument (HI) Foresight (FS) Elevation (Elev.) BM1 Backsight after BM1 Instrument after BM1 N/A Elevation of BM1 TP1 Backsight after TP1 Instrument after TP1 Foresight to TP1 Elevation of TP1 ... ... ... ... ... BMlast N/A N/A Foresight to BMlast Elevation of BMlast