Invert Level and Invert Elevation are one in the same. Invert Level = Invert Elevation (IE).

invert level =high level - the reading - the diameter of pipe

US = Up Stream invert level

DS= Down Stream invert level

If detailed on a manhole, the difference being the gradient of pipe in chamber from one end to the other.

Invert Level is the bottom of the pipe, reduced level is the middle of the pipe.

The invert level is the base interior level of a pipe, trench or tunnel; it can be considered the "floor" level. Conversely, the crown level is the highest interior level, and can be considered the "roof" level