28" of H2o is standard test depression.

Mine has a Dwyer 36" vertical manometer for test
depression and an extra 36" for pitot probes.
It has a Dwyer 6" incline manometer for taking
readings. You'll need more than one blower. (Mine
has eight) I haven't a clue what a magnahelic
needel gauge is though.

Try here for more information....... PTS Flowbench