Teledyne 200A Instruction Manual page 37

Teledyne API Model 200A NO Analyzer Instruction Manual, 02246, Rev. F1
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NOTE
On vacuum vs absolute pressure:
Many vacuum gauges read relative to ambient pressure, therefore
a reading of 25" of mercury (Hg) at sea level (which would give an
absolute pressure of about 5" Hg in the reaction cell) would read
only 20" Hg at high altitude sites. Therefore in this manual the vacuum
specification of 5" Hg pressure is given as an absolute pressure
- 5"Hg-A - reference against zero absolute pressure (a perfect vacuum)
thus removing ambiguities for high altitude sites.
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