<?php
/**
 * meter.ac t_dew calculations
 * 
 * t_raw is the measured ambient temperature
 * rh is the relative humidity
 */

$a=6.1121;
$d=234.5;
if ($t_raw < 0) {
        $b=17.966;
        $c=247.15;
}
else {
        $b=17.368;
        $c=238.88;
}
if ($rh > 0) {
        $gm = log( $rh*0.01*( pow(exp(1),(($b-(1*$t_raw)/$d)*((1*$t_raw)/($c+(1*$t_raw))))) ) );
}
else {
        $gm = log( 0.1*0.01*( pow(exp(1),(($b-(1*$t_raw)/$d)*((1*$t_raw)/($c+(1*$t_raw))))) ) );
}
$t_dew = round($c*(1*$gm)/($b-(1*$gm)), 1);
?>