# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Ah, give someone a calculator.......**

**From:**Gary LaPook

**Date:**2010 Aug 16, 18:22 +0200

This definition from the U.S. NOAA

**HectoPascals (hPa)**- 1 hPA= 1 millibar, a unit of pressure. See:

http://www.cpc.noaa.gov/products/outreach/glossary.shtml

Definition from Wiki:

The

**pascal**(symbol:

**Pa**) is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, name after the French mathematician, physicist, inventor, writer and Catholic philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre. In everyday life, the pascal is perhaps best known from meteorological barometric pressure reports, where it occurs in the form of hectopascals (1 hPa ≡ 100 Pa) or kilopascals (1 kPa ≡ 1000 Pa).

^{[1]}In other contexts, the kilopascal is commonly used, for example on bicycle tire labels.

^{[2]}One hectopascal corresponds to about 0.1% and one kilopascal to about 1% of atmospheric pressure (near sea level). One hectopascal is equivalent to one millibar; one standard atmosphere is exactly equal to 1013.25 hPa.

see:

http://en.wikipedia.org/wiki/Pascal_%28unit%29

This definition of bar from Wiki:

## Definition

The kilobar, bar, decibar, centibar, and millibar are defined as:

- 1 Kbar = 1000 bar = 100,000 kPa = 100,000,000 dyn/cm
^{2}= 100 MPa = 0.1 GPa - 1 bar = 100 kPa (kilopascals) = 1,000,000 dynes per square centimeter (baryes) = 0.987 atm (atmospheres) = 14.5038 psi = 29.53 inHg
- 1 dbar = 0.1 bar = 10 kPa = 100,000 dyn/cm
^{2} - 1 cbar = 0.01 bar = 1 kPa
- 1 mbar = 0.001 bar = 0.1 kPa = 1 hPa (hectopascal) = 1,000 dyn/cm
^{2}

Example conversion: 1 atm pressure = 1.01325 bar = 1.01325 x 10^{5}
Pa = 1.01325 x 10^{5} N/m^{2
}

^{
see:
}

^{http://en.wikipedia.org/wiki/Bar_%28unit%29
}

^{Neither the definition of the bar or of the pascal uses mass
units ,only units of force, dynes and newtons.
}

^{
gl
}

^{
}

^{
}

yrobinjo@noos.fr wrote:

By the way, I believe that figures in hPa and in mBar should not be 'exactly' the same.

Why ? Because of the difference between referentials : MKS for the first one (Kg as a mass) and MKpS (Kg as a force) for the second one. So there should be a factor of g = 9,81 (earth gravity mean acceleration) to be inserted : 1 Bar = 9,81 Pa (not exactly 10 Pa).

But this shift of 2% is commonly integrated.

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