function check(ad)
{
	var ch=ad.value;
	if(isNaN(ch))
	{
		var df=ch.substring(0,(ch.length-1))
		ad.value=df;
	}	
}

function calc()
{
	var o = document.cloud.opt1.value;
	var o2 = document.cloud.opt2.value;
	var t = document.cloud.t.value;
	var w = document.cloud.d.value;
	
		if(o=="f"){
			t = (t-32.0)*5.0/9.0;
			w = (w-32.0)*5.0/9.0;
		}
		if(o=="k"){
			t = t - 273.15;
			w = w - 273.15;
		}
		var x = (t-w)/0.00802;
		var y = -0.00984*x + t;

		

		if(o2=="k")
			x = x/1000.0;
		if(o2=="f")
			x = x*3.281;
		if(o2=="n")
			x = x*3.281/6076.115485564304;
		if(o2=="s")
			x = x*3.281/5280.0;
		
		if (o=="f")
			y = (y*9.0/5.0) + 32.0;
    		if (o=="k") 
			y = y + 273.15;

		document.cloud.r1.value = Math.round(x*100)/100;
		document.cloud.r2.value = Math.round(y*100)/100;
	
}