Why does the Pressure Drop and Mass-Averaged Reports give different values of pressure drop than the Heat Exchanger Dual Stream Report?

When post-processing results, it is sometimes important to understand which values specific reports take for calculations.
This is especially a source of confusion if two reports, for example pressure drop and heat exchanger dual stream reports, give different results. The question arises: which value is right?

The pressure drop report is a mass flow averaged report of difference of the total pressures on two surfaces.
 

It is important to note that values for flow boundaries are actual face values and are directly used in the equation. 
However, for general internal interfaces, boundary values are reconstructed from cell values and then used in the expression above. 
Values of pressure on internal interface boundaries with Porous Region on at-least one side are the cell values.

The Dual Stream Heat Exchanger report reports the area averaged pressure and temperature using the upwinded cell values.

It is advised to use dual stream heat exchanger as it should give more meaningful results for the heat exchanger interface. 

On general, whenever a specialized report exists for a certain application, it should be utilized to obtain the most accurate results, as the numerical methods and inputs that it uses is tailored for this application.