I hope this question doesn't have too obvious of an answer. Basically, I still cannot grasp why Bernoulli's equation applies for wind tunnels and pitot-static probes. According to my textbook ("Introduction to Flight" by Anderson), Bernoulli's equation holds only when comparing two points along a streamline. So, why does the equation apply to wind tunnels as a whole? Aren't wind tunnels made up of many streamlines? In addition, why can Bernoulli's equation be applied to pitot-static probes? Aren't the total pressure and static pressure being measured on two different streamlines? And if that is true, why does Bernoulli's equation hold? Please help, the text describes Bernoulli's equation as applying only to streamlines, but does not specify why it then applies to wind tunnels and pitot-static probes.