If obvert is selected, the top of the circle is placed at the elevation.

It was observed that a small amount of sediment accumulated at the downstream end of the perforated pipes, and some organic materials such as leaves were hung to the obvert of the perforated pipes.

The difference is that in its application to categorical propositions the result of contraposition is two contrapositives, each being the obvert of the other, i.e. "No non-P is S" and "All non-P is non-S".

Since in the process of contraposition the obverse can be obtained in all four types of traditional propositions, yielding propositions with the contradictory of the original predicate, contraposition is first obtained by converting the obvert of the original proposition.