It sounds like you are talking about a sewer system where the depth measurement is typically given as the distance from the ground surface to the invert (bottom) of the sewer pipe. However, in some cases, it may be more useful to measure the depth to the soffit (top) of the sewer pipe, particularly to ensure the sewer has sufficient cover. https://www.benefitscal.biz/

The depth to invert measurement is the most common measurement used for sewers, as it provides a direct measurement of the distance from the ground surface to the bottom of the pipe. However, in some situations, it may be necessary to use the depth to soffit measurement instead. This is particularly true in cases where the sewer pipe is not buried at a consistent depth throughout its length, or where the cover over the pipe is not consistent.

By measuring the depth to soffit, engineers and contractors can ensure that the sewer pipe has sufficient cover to protect it from damage, particularly from heavy traffic or other loads. This can be particularly important in areas where the soil is unstable or prone to settlement, as it can help prevent the pipe from sagging or collapsing.

Overall, the choice between measuring depth to invert or depth to soffit will depend on the specific circumstances of the sewer system and the goals of the project.

But it must please label clearly which one it is doing. If it just says "depth" we will all be wasting a lot of time manually checking the levels with a calculator - or worse, forgetting to check and making mistakes.