#!/usr/bin/perl 

(! scalar @ARGV) && die "usage: $0 tempC %RH\n";

# Tc = temp C  RH = %RH

my ($Tc,$RH,$foo) = @ARGV;

my $Es = 6.11*10.0**(7.5*$Tc/(237.7+$Tc));

# The next step is to use the saturation vapor pressure and the relative
# humidity to compute the actual vapor pressure(E) of the air. This can be done
# with the following formula.

my $E=($RH*$Es)/100;


# RH=relative humidity of air expressed as a percent.(i.e. 80%)

#Now you are ready to use the following formula to obtain the dewpoint
#temperature.

#Tdc = temp dew C

my $Tdc = (-430.22+237.7*log($E))/(-log($E)+19.08);

print "Temp $Tc  RH $RH  is dewpoint of $Tdc\n";