function DP(dewpoint){
  var A = 8.1332;
  var B = 1762.39;
  var C = 235.66;
  var u1 = dewpoint.corf[0].checked;
  var u2 = dewpoint.corf[1].checked;
  var u3 = dewpoint.corf[2].checked;


  if (u1 == true) {

    var ta = parseInt((dewpoint.airtemp.value-32)/1.8);

	} else {
	if (u3 == true) {
	  var ta = parseInt(dewpoint.airtemp.value-273.14);

	} else {

	  var ta = parseInt(dewpoint.airtemp.value);

    }
  }
  var rh = parseInt(dewpoint.relhum.value);
  var pa1 = A - B /(ta + 235.66);
  var pa = Math.pow(10, pa1);
  var tdp1 = (rh * pa)/100;
  var tdp = Math.log(tdp1) ;
  var dp3 = tdp/Math.LN10;
  var dp2 = B / (dp3 - A);
  var dp = Math.round(- dp2 - 235.66);

    if (u1 == true) {

    res = dp *1.8+32;
    	} else {
	if (u3 == true) {

           res = dp + 273.14;

	} else {

	   res = dp;

    }
  }

  dewpoint.dewpointres.value = (Math.round(res*10))/10;

}
function cleardewpoint(form){
form.relhum.value = "";
form.airtemp.value = "";
form.dewpointres.value = "";
}