I was just experimenting with the Chandler Burning Index, I found the following formula to calculate it:
CBI = (((110 - 1.373*RH) - 0.54 * (10.20 - T)) * (124 * 10^(-0.0142*RH)))/60
RH - humidity in %, T = temp in deg C
in PHP I used:
(((110 - 1.373 * $RH) - 0.54 * (10.20 - $T)) * (124 * pow(10,(-0.0142 * $RH))))/60;
Now the problem is, that when for example I plug in 97% for humidity and 19.4 C for temperature, I get a negative number... and likewise, some numbers lead to CBI way above 100. But the index description says it should lie between 0 and 100. I even checked this by manually calculating it on a calculator and that formula really gives these values.
Is my formula incorrect? Or can the values be negative and above 100?