function isLength()
{
var str = document.forms[0].length.value;
if (str == "")
	{
	alert("\nPlease enter the length of your fish.")
	document.forms[0].elements[1].focus();
	return false;
	}
	isChecked();
return true;
}

function isChecked()
{
var a = document.forms[0].F1.checked;
var b = document.forms[0].F2.checked;
var c = document.forms[0].F3.checked;
var d = document.forms[0].F4.checked;
var e = document.forms[0].F5.checked;
var f = document.forms[0].F6.checked;
if (a+b+c+d+e+f == "")
{
	alert("\nPlease select the fish species.")
	document.forms[0].elements[1].focus();
	return false;
	}
	
	if (a+b+c+d+e+f != 1)
{
	alert("\nPlease reset the calculator and select only one species")
	document.forms[0].elements[1].focus();
	return false;
	}
	calcweight(document.forms[0]);
return true;
}

	function calcweight(form)
		{
		var constant = 1 
		if (form.girth.value < 1){
			form.girth.value = 0.58 * form.length.value
			}
		if (form.F1.checked == "1"){
			form.weight.value = eval(form.length.value * form.length.value * form.length.value / 3500)
			}
		if (form.F2.checked == "1"){
			form.weight.value = eval(form.length.value * form.length.value * form.length.value / 2700)
			}
		if (form.F3.checked == "1"){
			form.weight.value = eval(form.length.value * form.length.value * form.length.value / 1200)
			}
		if (form.F4.checked == "1"){
			form.weight.value = eval(form.length.value * form.length.value * form.girth.value / 1020)
			}
		if (form.F5.checked == "1"){
			form.weight.value = eval(form.length.value * form.girth.value * form.girth.value / 800)
			}
		if (form.F6.checked == "1"){
			form.weight.value = eval(form.length.value * form.girth.value * form.girth.value / 900)
			}
		}