The location of the instrument tappings in process viewpoint

Try to allow for as many pipe diameters as possible before and after your tappings, 5-10 minimum if your readings are important. If they are just for daily reporting you can put them closer but put a valve in the tapping lines just in case you need to dampen your input signals.

Mike

Depending what you need them for, don't they prescribe where you should put them?

I always thought that any aperture, or change in, caused a pressure differential over that item. This means that up and down stream of a choke valve, you will find pressure irregularities that do not transpose to the nominal pressure in the whole of the pipe. Also the same with bends and branches.