Air density calculation

This function calculates the density of the air

This function calculates the air-density based on the papers:

1)'Equation for the Determination of the Density of Moist Air'
P.Giacomo, Metrologia 18, 33-40 (1982)

2)'Equation for the Determination of the Density of Moist Air'
R.S. Davis Metrologia 29, 67-70 (1992)

Parameters:
t = ambient temperature (ºC)
hr = relative humidity [%]
p = ambient pressure [Pa]

ver 1.0
06/10/2006 Jose Luis Prego Borges
Sensor & System Group, Universitat Politecnica de Catalunya, Spain