Work out level loop misclosure instantly with clear inputs, formula shown and shareable results.
In a closed level loop the sum of backsights minus the sum of foresights should equal the change in level, which is zero for a loop returning to its start. Any residual is the misclosure. Allowable misclosure grows with the square root of loop length because random errors accumulate in that way, with the constant set by the order of levelling.
Misclosure
Misclosure = sum of backsights - sum of foresights
Allowable
Allowable mm = constant x sqrt(loop length in km), typically 12 mm for ordinary work
Misclosure = sum of backsights - sum of foresights. In a closed level loop the sum of backsights minus the sum of foresights should equal the change in level, which is zero for a loop returning to its start.
In proportion to the distance or the number of setups between benchmarks, applied with opposite sign to the misclosure so the loop closes exactly.
This calculator takes 4 inputs: Sum of backsights, Sum of foresights, Loop length, Allowable misclosure constant. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.