please see http://www.proz.com/?sp=h&id=36131 (Carla Zwanenberg, Mar 6, 2001) : *Mechanische vacuümmeters. Bourdon buisveer manometer: platte gebogen buis met elliptische doorsnede, gemaakt van metaal en zo dun dat hij veren kan....*

BOURDON Vacuum Gauge
The inside of a tube which is bent into a circular arc (the so-called Bourdon tube) is connected to the vacuum system. Due to the effect of the external atmospheric pressure, the end of the tube bends more
or less during the evacuation process. This actuates the pointer
arrangement which is attached to this point. The correspond-ing pressure can be read off on a linear scale. With Bourdon gauges it is possible to roughly determine pressures between 10 mbar (7.5 Torr) and atmospheric pressure. Pressure sensors, manometers or Bourdon gauges other than those supplied can be calibrated over the range 20 kNm -2 to 200 kNm -2 .
www.armfield.co.uk/pdf_files/th2.pdf

In 1849 the Bourdon tube pressure gauge was patented in France by Eugene Bourdon. It is still one of the most widely used instruments for measuring the pressure of liquids and gases of all kinds, including steam, water, and air up to pressures of 100,000 pounds per square inch. Eugene Bourdon founded the Bourdon Sedeme Company to manufacture his invention.

The American patent rights to Eugene Bourdon's gauge were bought by Edward Ashcroft in 1852. Ashcroft played an important role in the widespread adoption of steam power in this country. He renamed Bourdon's gauge, the Ashcroft gauge. http://inventors.about.com/library/inventors/blbourdon.htm