[Paraview] PV 3.10.1 integration over a surface

[Stephen Wornom]

How does one compute the integral of P Normal ds ? 
where Normal is the surface normal vector 

click on integrate variables computes the integral of P ds 
I would like 
Fx = integral of P nx ds 
where nx ds is the surface area normal to the x-direction. 
Hope my question is clear. 
Stephen 
p.s. 
The surface in question is a cylinder 
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