Estimating volume of separated surfaces, plotting histogram

@Kenneth_Moreland Thanks so much for helping us see how to make histograms that show those field values!

I’ll also do some snooping about the surfaces that seem to be failing the check. I was searching and it sounds like the algorithm that is calculating volume relies on the direction of a normal vector which in some cases might be pointing the wrong way? Negative cell volume

@spyridon97 thanks for also jumping in. Let me get you a collection of the data.