// Field of view calculator
			// Script written by Dave Fisher - 5/1/99
			// Evaluates lens format selection
			function lens_format(){
				if (document.lenscalc.radio1[0].checked){
				quarter_format()
				}
				else if (document.lenscalc.radio1[1].checked){
				third_format()
				}
				else if (document.lenscalc.radio1[2].checked){
				half_format()
				}
				else if (document.lenscalc.radio1[3].checked){
				twothirds_format()
				}
				else if (document.lenscalc.radio1[4].checked){
				oneinch_format()
				}
				else {
				}
			//Performs calculations for quarter inch formats
			function quarter_format(){
				var distance = document.lenscalc.distance.value
				var horizontal = document.lenscalc.horizontal.value
				var lens_size = document.lenscalc.lens_size.value
				var vertical = document.lenscalc.vertical.value

				if ((distance > 0) && (horizontal > 0) && (vertical == 0) && (lens_size == 0)){
  				lens_size = distance/horizontal*3.6
				vertical = horizontal*.75
   				document.lenscalc.lens_size.value = RoundOff(lens_size)
				document.lenscalc.vertical.value = RoundOff(vertical)
   				}

				else if ((distance > 0) && (horizontal == 0) && (vertical == 0) && (lens_size > 0)){
				horizontal = distance/lens_size*3.6
				vertical = horizontal*.75
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				document.lenscalc.vertical.value = RoundOff(vertical)
				}

				else if ((distance == 0) && (horizontal > 0) && (vertical == 0) && (lens_size > 0)){
				distance = horizontal/3.6*lens_size
				vertical = horizontal*.75
				document.lenscalc.distance.value = RoundOff(distance)
				document.lenscalc.vertical.value = RoundOff(vertical)
				}

				else if ((distance == 0) && (horizontal == 0) && (vertical > 0) && (lens_size > 0)){
				distance = vertical/2.7*lens_size
				horizontal = vertical/3*4
				document.lenscalc.distance.value = RoundOff(distance)
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				}

				else if ((distance > 0) && (horizontal == 0) && (vertical > 0) && (lens_size == 0)){
				horizontal = vertical/3*4
				lens_size = distance/horizontal*3.6
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				document.lenscalc.lens_size.value = RoundOff(lens_size)
				}

				else {alert("One or more of your answers was invalid. Please try again.")}
				}
			//Performs calculations for third inch formats
			function third_format(){
				var distance = document.lenscalc.distance.value
				var horizontal = document.lenscalc.horizontal.value
				var lens_size = document.lenscalc.lens_size.value
				var vertical = document.lenscalc.vertical.value

				if ((distance > 0) && (horizontal > 0) && (vertical == 0) && (lens_size == 0)){
  				lens_size = distance/horizontal*4.8
				vertical = horizontal*.75
   				document.lenscalc.lens_size.value = RoundOff(lens_size)
				document.lenscalc.vertical.value = RoundOff(vertical)
   				}

				else if ((distance > 0) && (horizontal == 0) && (vertical == 0) && (lens_size > 0)){
				horizontal = distance/lens_size*4.8
				vertical = horizontal*.75
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				document.lenscalc.vertical.value = RoundOff(vertical)
				}

				else if ((distance == 0) && (horizontal > 0) && (vertical == 0) && (lens_size > 0)){
				distance = horizontal/4.8*lens_size
				vertical = horizontal*.75
				document.lenscalc.distance.value = RoundOff(distance)
				document.lenscalc.vertical.value = RoundOff(vertical)
				}

				else if ((distance == 0) && (horizontal == 0) && (vertical > 0) && (lens_size > 0)){
				distance = vertical/3.6*lens_size
				horizontal = vertical/3*4
				document.lenscalc.distance.value = RoundOff(distance)
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				}

				else if ((distance > 0) && (horizontal == 0) && (vertical > 0) && (lens_size == 0)){
				horizontal = vertical/3*4
				lens_size = distance/horizontal*4.8
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				document.lenscalc.lens_size.value = RoundOff(lens_size)
				}

				else {alert("One or more of your answers was invalid. Please try again.")}
				}
			//Performs calculations for half inch formats
			function half_format(){
				var distance = document.lenscalc.distance.value
				var horizontal = document.lenscalc.horizontal.value
				var lens_size = document.lenscalc.lens_size.value
				var vertical = document.lenscalc.vertical.value

				if ((distance > 0) && (horizontal > 0) && (vertical == 0) && (lens_size == 0)){
  				lens_size = distance/horizontal*6.4
				vertical = horizontal*.75
   				document.lenscalc.lens_size.value = RoundOff(lens_size)
				document.lenscalc.vertical.value = RoundOff(vertical)
   				}

				else if ((distance > 0) && (horizontal == 0) && (vertical == 0) && (lens_size > 0)){
				horizontal = distance/lens_size*6.4
				vertical = horizontal*.75
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				document.lenscalc.vertical.value = RoundOff(vertical)
				}

				else if ((distance == 0) && (horizontal > 0) && (vertical == 0) && (lens_size > 0)){
				distance = horizontal/6.4*lens_size
				vertical = horizontal*.75
				document.lenscalc.distance.value = RoundOff(distance)
				document.lenscalc.vertical.value = RoundOff(vertical)
				}

				else if ((distance == 0) && (horizontal == 0) && (vertical > 0) && (lens_size > 0)){
				distance = vertical/4.8*lens_size
				horizontal = vertical/3*4
				document.lenscalc.distance.value = RoundOff(distance)
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				}

				else if ((distance > 0) && (horizontal == 0) && (vertical > 0) && (lens_size == 0)){
				horizontal = vertical/3*4
				lens_size = distance/horizontal*6.4
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				document.lenscalc.lens_size.value = RoundOff(lens_size)
				}

				else {alert("One or more of your answers was invalid. Please try again.")}
				}
			//Performs calculations for two thirds inch formats
			function twothirds_format(){
				var distance = document.lenscalc.distance.value
				var horizontal = document.lenscalc.horizontal.value
				var lens_size = document.lenscalc.lens_size.value
				var vertical = document.lenscalc.vertical.value

				if ((distance > 0) && (horizontal > 0) && (vertical == 0) && (lens_size == 0)){
  				lens_size = distance/horizontal*8.8
				vertical = horizontal*.75
   				document.lenscalc.lens_size.value = RoundOff(lens_size)
				document.lenscalc.vertical.value = RoundOff(vertical)
   				}

				else if ((distance > 0) && (horizontal == 0) && (vertical == 0) && (lens_size > 0)){
				horizontal = distance/lens_size*8.8
				vertical = horizontal*.75
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				document.lenscalc.vertical.value = RoundOff(vertical)
				}

				else if ((distance == 0) && (horizontal > 0) && (vertical == 0) && (lens_size > 0)){
				distance = horizontal/8.8*lens_size
				vertical = horizontal*.75
				document.lenscalc.distance.value = RoundOff(distance)
				document.lenscalc.vertical.value = RoundOff(vertical)
				}

				else if ((distance == 0) && (horizontal == 0) && (vertical > 0) && (lens_size > 0)){
				distance = vertical/6.6*lens_size
				horizontal = vertical/3*4
				document.lenscalc.distance.value = RoundOff(distance)
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				}

				else if ((distance > 0) && (horizontal == 0) && (vertical > 0) && (lens_size == 0)){
				horizontal = vertical/3*4
				lens_size = distance/horizontal*8.8
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				document.lenscalc.lens_size.value = RoundOff(lens_size)
				}

				else {alert("One or more of your answers was invalid. Please try again.")}
				}
			//Performs calculations for one inch formats
			function oneinch_format(){
				var distance = document.lenscalc.distance.value
				var horizontal = document.lenscalc.horizontal.value
				var lens_size = document.lenscalc.lens_size.value
				var vertical = document.lenscalc.vertical.value

				if ((distance > 0) && (horizontal > 0) && (vertical == 0) && (lens_size == 0)){
  				lens_size = distance/horizontal*12.8
				vertical = horizontal*.75
   				document.lenscalc.lens_size.value = RoundOff(lens_size)
				document.lenscalc.vertical.value = RoundOff(vertical)
   				}

				else if ((distance > 0) && (horizontal == 0) && (vertical == 0) && (lens_size > 0)){
				horizontal = distance/lens_size*12.8
				vertical = horizontal*.75
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				document.lenscalc.vertical.value = RoundOff(vertical)
				}

				else if ((distance == 0) && (horizontal > 0) && (vertical == 0) && (lens_size > 0)){
				distance = horizontal/12.8*lens_size
				vertical = horizontal*.75
				document.lenscalc.distance.value = RoundOff(distance)
				document.lenscalc.vertical.value = RoundOff(vertical)
				}

				else if ((distance == 0) && (horizontal == 0) && (vertical > 0) && (lens_size > 0)){
				distance = vertical/9.6*lens_size
				horizontal = vertical/3*4
				document.lenscalc.distance.value = RoundOff(distance)
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				}

				else if ((distance > 0) && (horizontal == 0) && (vertical > 0) && (lens_size == 0)){
				horizontal = vertical/3*4
				lens_size = distance/horizontal*12.8
				document.lenscalc.horizontal.value = RoundOff(horizontal)
				document.lenscalc.lens_size.value = RoundOff(lens_size)
				}

				else {alert("One or more of your answers was invalid. Please try again.")}
				}
				}
			function RoundOff(s)
				{
				return Math.round(s*10)/10
				}