Pipe tallies, casing setting depths, and most drilling reports are in measured depth. The difference between two measured depths is the length of hole between them, which is the length of casing or tubing that has to cover that interval.
It is not a vertical depth. Dogleg severity, surveys, and the length of the drill string all live in measured depth. Pressure gradients do not. A formation top picked in measured depth has to be converted before it is posted on a structure map.