Mark out Analysis

Hello;

Could anyone share a little detailed idea of how to conduct markout analysis.

Mark out as I understand is, using different time frames to see if you would have held the position how much + or - pnl could be

But my question is, what position do you consider - the current netpos or its calculated from every execution ? (Think hft when positions change frequently)

And for price should one go with mid point ?

I am trying to do this for fx futures and not equity so any examples using that would help or for that matter any white paper or link

Thanks