Differential Leveling (HI Method) and Loop Misclosure
Carries an elevation from a benchmark across a site.
Example
You enter
- Benchmark elevation (ft) 100
- Backsight readings (ft) 4.32, 5.6
- Foresight readings (ft) 2.15, 3.4
- Known close 104.4
You get
- Final elevation 104.37 ft
- Loop misclosure -0.03
Details, formula, and sources
Differential leveling reduces backsight/foresight rod readings by the height-of-instrument method (HI = elev + BS, elev = HI - FS), and checks a loop for misclosure. A BM at 100.00 ft with backsights 4.32 / 5.60 and foresights 2.15 / 3.40 closes at 104.37 ft, the sum(BS) - sum(FS) rise the field book is balanced against; close on a known 104.40 and the -0.03 ft misclosure is the pass/fail. Arithmetic reduction, no adjustment distribution. A computational aid; the project control governs.
HI_i = elev_(i-1) + BS_i; elev_i = HI_i - FS_i; final_elev = bm + sum(BS) - sum(FS); misclosure = final_elev - known_close.
The height-of-instrument differential-leveling reduction and the loop-misclosure check, as compiled in the standard surveying references (Ghilani/Wolf, Elementary Surveying), by name.
The HI leveling method and the loop-misclosure check are public surveying results; FM 5-233 (Construction Surveying) is a public-domain US Government reference.
Estimate. AHJ and licensed professional govern.
Field names used by the API: bm_elev, bs, fs, known_close, final_elev, misclosure
- HI method HI = elev + BS, elev = HI - FS; elevation change = sum(BS) - sum(FS)Ghilani/Wolf Elementary Surveying
- Misclosure computed closing elevation minus the known closing elevation on a loopleveling practice
- No adjustment the misclosure is not distributed back through the turning points herescope of this tile