Well i got a very nice gauge from a british company. sadly i cant find the company anywhere online except for a few exerpts. This one has .001 resolution measured in bars.. it also has two inputs and does pressure differential. if you dont hook one up u just get pressure relative to ambient which is nice becuase it is self calibrating to ambient.
um back to something useful to yourself. I noticed that pH uses a pressure differential meter. the one he uses looks alot like the one below. either way rosemount sells units for this purpose.
http://cgi.ebay.com/ws/eBayISAPI.dll...513380956&rd=1