How to measure the pressure inside a pipeline segment?

Simple question.

How to measure the pressure in the pipeline segment?
I'm not sure how to measure it, but I think that measuring only 1 spot of pipeline section may provide us with wrong information depending on the flow regime inside.

For instance, if the flow regime inside is stratified flow, pressure of liquid section would be different from that of gas section...

Same thing may go with temperature, I guess.

It would be helpful if someone can give me a brief explanation (, of course, longer one is better :)) about the phenomenon inside the pipeline with measuring instrument.

Thanks in advance.

Hmmm one way would be to send a real skiny operator with a gouge through the pig launcher. If you want to meassure the temperature you give him a thermometer also.
Another way is to estimate them based on pressures, fluid properties, PL properties etc. but this method requires expertise and its more difficult.