We have tracked down his original extensive technical report on the development of this device , which we will make into a pdf ebook that is inexpensive and easy to access. (For now it is too big, and takes some cleaning up.)
The history of this device is quite fascinating, and seems to be an example of some lack of communications between researchers–at least several of the key players do not reference each other during the days of its development. See for example the early work of Miksad  and a related patent app  filed in 1989, canceled in 1996... maybe there is a story there as well!
As should not be surprising, the best of the devices comes from Paroscientific, our neighbors just across the bridge in Redmond, WA. They are the world leader in all matters relating to high accuracy barometric pressure measurement.  Paroscientific has somewhere online at their website a report of the testing of this device, but we have not found this yet.
And we should of course mention Vaisala, the world leader in production of the full range of weather instrumentation, which has a top of the line model as well . These devices are often refereed to as static pressure ports, without reference to Gill, but it seems he was a pioneer in the development of the engineering.
For completeness, note that the pressure port requirement has applications in other areas, such as pressure drop measurements in air conditioning conduits where there is a varying wind flow through the system .
THIS ARTICLE IS A WORK IN PROGRESS. IF YOU HAVE AN IMMEDIATE NEED FOR MORE DETAIL, LET US KNOW AND WE WILL PUSH IT UP THE LIST. FOR NOW I JUST WANTED TO COMPILE THE PIECES WE HAVE SO WE HAVE A REMINDER TO MAKE THE GILL EBOOK... which is in keeping with one of our ebook goals, to preserve obscure but important texts that somehow Google did not do for us.
 Guide to Meteorological Instruments and Observing Practices, WMO-8 (related section cited in , below. Many copies of the full document online.)
 The Barometer Handbook
 RM Young model 61002
 Development and Testing of a No-moving-parts Static Pressure Inlet for Use on Ocean Buoys, Gerald C. Gill 1975-76. 120 pages. [To be available shortly in full. Contact us if you need it earlier.]
 An Omini Directional Static Pressure Port, Richard Miksad, 1975-76
 Pressure Port Patent app (I do not know where we found this. It was part of the research for the Barometer Handbook. It at least shows the insides of one design, as does the Gill original article. We will, of course, never see the insides of the RM Young or Paroscientifc models online, unless we buy one and take it apart.)
 Paroscientific precision pressure port model 8007 (manual)
 Vaisala Static Pressure Head SPH10 / SPH20
 An Inexpensive Method for Measurements of Static Pressure Fluctuations, Liberzon and Shemer, 2009