function blankdimension(shape){
	if (shape == "circle") {
		document.getElementById("radius").value = "";
	}
	else if (shape == "rect" || shape == "elipse" || shape == "triangle" || shape == "paral") {
		document.getElementById("base").value = "";
		document.getElementById("height").value = "";
	}
	else if (shape == "trap") {
		document.getElementById("base1").value = "";
		document.getElementById("base2").value = "";
		document.getElementById("height").value = "";
	}
   	document.getElementById("totlbs").value = ""
   	document.getElementById("totbags").value = ""
}

function blanktotal (){
   	document.getElementById("total").value = ""
   	document.getElementById("totlbs").value = ""
   	document.getElementById("totbags").value = ""
}

function blankfert (){
   	document.getElementById("totlbs").value = ""
   	document.getElementById("totbags").value = ""
}

function roundn (z1) {
	var n1 = 0;
        n1 = Math.round(z1 * 100);
	var n2 = n1 / 100;
	z2 = n2;
	return z2;
}

function chknumber(nameid,name1,maxval){

	var val1 = document.getElementById(nameid).value;

	var ok = 0;

	if (val1 > 0 && val1 <= maxval ) {
		ok = 1;
	}

	if (ok == 0) {
		alert (name1 + " must be a number greater than 0 to " + maxval);
		document.getElementById(nameid).value;
		document.getElementById(nameid).focus();
	}
	else if (nameid=="n" && val1 > 30) {
		alert ("Nitrogyn value seems high: Please doublecheck");
	}
}

function calc(shape){
   var r = 0;
   var b = 0;
   var b1 = 0;
   var b2 = 0;
   var h = 0;
   var t = 0;
   var t2 = 0
   if (shape == "circle") {
   	r = document.getElementById("radius").value;
   	if (r > 0) {
   	   t = (22/7) * (r*r);
	   t=roundn(t);
   	   document.getElementById("total").value = t;
   	}
   	else {
	   alert ("r is invalid")
	}
   }
   else if (shape == "rect" || shape == "elipse" || shape == "triangle" || shape == "paral") {
   	b = document.getElementById("base").value; 
   	h = document.getElementById("height").value;
   	if (b > 0 && h > 0) {
		if (shape == "rect" || shape == "paral") {
   			t = b * h;
		}
		else if (shape == "elipse") {
   			t = (22/7) * (b * h);
		}
		else if (shape == "triangle") {
   			t = (b * h) / 2;
		}
		t = roundn(t);
   	   	document.getElementById("total").value = t;
   	}
   	else {
		alert ("b or h is invalid")
   	}
   }
   else if (shape == "trap") {
   	b1 = document.getElementById("base1").value; 
   	b2 = document.getElementById("base2").value; 
   	h = document.getElementById("height").value;
   	if (b1 > 0 && b2 > 0 && h > 0) {
		t = ((b1 * h) + (b2 * h))/2;
		t = roundn(t);
   	   	document.getElementById("total").value = t;
   	}
   	else {
		alert ("b1 or b2 or h is invalid")
   	}
   }
}

function calcfert(){
   var n = 0;
   var lbs = 0;
   var area = 0;
   var tlbs = 0;
   var tbags  = 0;
   n 	= document.getElementById("n").value; 
   lbs = document.getElementById("lbs").value; 
   area = document.getElementById("total").value; 
   if (n > 0 && lbs > 0 && area > 0) {
   	tlbs = (area/1000)/(n/100);
   	tbags = tlbs/lbs;
	tlbs=roundn(tlbs);
	tbags=roundn(tbags);
   	document.getElementById("totlbs").value = tlbs;
   	document.getElementById("totbags").value = tbags;
   }
   else if (n > 0 && lbs > 0) {
	alert ("You must first calculate the square footage")
   }
   else if (area > 0) {
	alert ("N or pounds is missing")
   }
   else {
	alert ("N, pounds, or square footage is missing")
   }
}