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The pound per square inch absolute (psia) is used to make it clear that the pressure is relative to a vacuum rather than the ambient atmospheric pressure. Since atmospheric pressure at sea level is around 14.7 psi (101 kilopascals ), this will be added to any pressure reading made in air at sea level .
The SI unit for pressure is the pascal (Pa), equal to one newton per square metre (N/m 2, or kg·m −1 ·s −2). This name for the unit was added in 1971; [7] before that, pressure in SI was expressed in newtons per square metre. Other units of pressure, such as pounds per square inch (lbf/in 2) and bar, are also in common use.
+1.9 psi High air pressure for human lung, measured for trumpet player making staccato high notes [48] < +16 kPa +2.3 psi Systolic blood pressure in a healthy adult while at rest (< 120 mmHg) (gauge pressure) [44] +19.3 kPa +2.8 psi High end of lung pressure, exertable without injury by a healthy person for brief times [citation needed] +34 kPa ...
K-Factors have also previously been calculated and published using the United States customary units of pound per square inch (psi) and gallon per minute (gpm). Within the United States, US measurements are still often used instead of metric. [3] [4]
The pound per square inch (psi) is still in widespread use in the US and Canada, for measuring, for instance, tire pressure. A letter is often appended to the psi unit to indicate the measurement's zero reference; psia for absolute, psig for gauge, psid for differential, although this practice is discouraged by the NIST. [3]
In North America, air and other industrial gases are often measured in inches of water when at low pressure. This is in contrast to inches of mercury or pounds per square inch (psi, lbf/in 2) for larger pressures. One usage is in the measurement of air ("wind") that supplies a pipe organ and is referred simply as inches.
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Pound per square inch, unit of pressure; PSI (computational chemistry), software; J/psi meson, subatomic particle; Porous silicon; Water potential, denoted Ψ, in physical chemistry, the potential energy of a water solution relative to pure water; Wave function, denoted ψ, in quantum mechanics