Leveling Survey Calculator

How leveling is calculated

Subtract the sum of foresights from the sum of backsights. Add this signed elevation difference to the starting elevation. A larger backsight sum means that the final point is higher. For a single instrument setup, enter the two staff readings directly.

Example and limits

A starting elevation of 100 m, backsight sum of 3.85 m and foresight sum of 1.59 m give a rise of 2.26 m and an end elevation of 102.26 m. Intermediate sights must not be included in these sums. This arithmetic check does not replace field records, closure checks or network adjustment. Use a common datum and check the instrument in the field.

From field book to inputs

For several instrument setups, add each backsight to the backsight sum and each foresight to the foresight sum. A turning point connects successive setups. Its two readings belong in different columns. Intermediate sights used to calculate other point elevations do not belong in either sum. Counting an intermediate reading again as a foresight changes the transferred elevation.

For example, start at 50 m. At the first setup, a backsight of 1.20 m and a foresight of 0.80 m give a turning point elevation of 50.40 m. At the second setup, take a backsight of 0.90 m and a foresight of 1.40 m. This gives a fall of 0.50 m, so the end elevation is 49.90 m. Entering a backsight sum of 2.10 m and a foresight sum of 2.20 m gives a total difference of minus 0.10 m.

A negative elevation difference is not itself an error. It means the final point is lower. A normal upright staff reading, however, is not entered as negative. Negative elevation and negative staff reading are different concepts.

If the run ends at a known elevation, inspect the difference between calculated and known elevation separately. The calculator neither distributes this closure error nor selects an acceptance tolerance. Record the survey route, sight lengths and datum. The result remains a preliminary geometric calculation, not confirmation of field setting out.