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The torr is defined as 1 / 760 of one standard atmosphere, while the atmosphere is defined as 101325 pascals. Therefore, 1 Torr is equal to 101325 / 760 Pa. The decimal form of this fraction ( 133.322 368 421 052 631 578 947 ) is an infinitely long, periodically repeating decimal ( repetend length: 18).
Extreme-high vacuum [6] ... 1 torr ≈ 1 mmHg [34] ±200 Pa ... tensile strength of Inconel 625 according to Aircraft metal strength tables and the Mil-Hdbk-5 [80] 5. ...
Within each table, ... ≡ Distance light travels in one second in vacuum ... ≡ 13 595.1 kg/m 3 × 1 μm × g 0 ≈ 0.001 torr ≈ 0.133 3224 Pa [33] millimetre of ...
Vacuum quality is subdivided into ranges according to the technology required to achieve it or measure it. These ranges were defined in ISO 3529-1:2019 as shown in the following table (100 Pa corresponds to 0.75 Torr; Torr is a non-SI unit):
The first table shows exact conversion factors. This format emphasizes the underlying simplicity of the SI, and shows clearly why the conversion factors for Torr and mmHg are different: The second table gives approximate conversion factors (to six significant figures). This is the format that is used in practice.
Valid results within the quoted ranges from most equations are included in the table for comparison. A conversion factor is included into the original first coefficients of the equations to provide the pressure in pascals (CR2: 5.006, SMI: -0.875). Ref. SMI uses temperature scale ITS-48.
A vacuum gauge is used to measure pressures lower than the ambient atmospheric pressure, which is set as the zero point, in negative values (for instance, −1 bar or −760 mmHg equals total vacuum). Most gauges measure pressure relative to atmospheric pressure as the zero point, so this form of reading is simply referred to as "gauge pressure".
One langmuir corresponds to an exposure of 10 −6 Torr during one second. [1] [2] For example, exposing a surface to a gas pressure of 10 −8 Torr for 100 seconds corresponds to 1 L. Similarly, keeping the pressure of oxygen gas at 2.5·10 −6 Torr for 40 seconds will give a dose of 100 L.